[dev.fuzz] all: merge master (65f0d24) into dev.fuzz

[gostls13.git] / src / testing / testing.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package testing provides support for automated testing of Go packages.
// It is intended to be used in concert with the "go test" command, which automates
// execution of any function of the form
//     func TestXxx(*testing.T)
// where Xxx does not start with a lowercase letter. The function name
// serves to identify the test routine.
//
// Within these functions, use the Error, Fail or related methods to signal failure.
//
// To write a new test suite, create a file whose name ends _test.go that
// contains the TestXxx functions as described here. Put the file in the same
// package as the one being tested. The file will be excluded from regular
// package builds but will be included when the "go test" command is run.
// For more detail, run "go help test" and "go help testflag".
//
// A simple test function looks like this:
//
//     func TestAbs(t *testing.T) {
//         got := Abs(-1)
//         if got != 1 {
//             t.Errorf("Abs(-1) = %d; want 1", got)
//         }
//     }
//
// Benchmarks
//
// Functions of the form
//     func BenchmarkXxx(*testing.B)
// are considered benchmarks, and are executed by the "go test" command when
// its -bench flag is provided. Benchmarks are run sequentially.
//
// For a description of the testing flags, see
// https://golang.org/cmd/go/#hdr-Testing_flags.
//
// A sample benchmark function looks like this:
//     func BenchmarkRandInt(b *testing.B) {
//         for i := 0; i < b.N; i++ {
//             rand.Int()
//         }
//     }
//
// The benchmark function must run the target code b.N times.
// During benchmark execution, b.N is adjusted until the benchmark function lasts
// long enough to be timed reliably. The output
//     BenchmarkRandInt-8       68453040                17.8 ns/op
// means that the loop ran 68453040 times at a speed of 17.8 ns per loop.
//
// If a benchmark needs some expensive setup before running, the timer
// may be reset:
//
//     func BenchmarkBigLen(b *testing.B) {
//         big := NewBig()
//         b.ResetTimer()
//         for i := 0; i < b.N; i++ {
//             big.Len()
//         }
//     }
//
// If a benchmark needs to test performance in a parallel setting, it may use
// the RunParallel helper function; such benchmarks are intended to be used with
// the go test -cpu flag:
//
//     func BenchmarkTemplateParallel(b *testing.B) {
//         templ := template.Must(template.New("test").Parse("Hello, {{.}}!"))
//         b.RunParallel(func(pb *testing.PB) {
//             var buf bytes.Buffer
//             for pb.Next() {
//                 buf.Reset()
//                 templ.Execute(&buf, "World")
//             }
//         })
//     }
//
// Examples
//
// The package also runs and verifies example code. Example functions may
// include a concluding line comment that begins with "Output:" and is compared with
// the standard output of the function when the tests are run. (The comparison
// ignores leading and trailing space.) These are examples of an example:
//
//     func ExampleHello() {
//         fmt.Println("hello")
//         // Output: hello
//     }
//
//     func ExampleSalutations() {
//         fmt.Println("hello, and")
//         fmt.Println("goodbye")
//         // Output:
//         // hello, and
//         // goodbye
//     }
//
// The comment prefix "Unordered output:" is like "Output:", but matches any
// line order:
//
//     func ExamplePerm() {
//         for _, value := range Perm(5) {
//             fmt.Println(value)
//         }
//         // Unordered output: 4
//         // 2
//         // 1
//         // 3
//         // 0
//     }
//
// Example functions without output comments are compiled but not executed.
//
// The naming convention to declare examples for the package, a function F, a type T and
// method M on type T are:
//
//     func Example() { ... }
//     func ExampleF() { ... }
//     func ExampleT() { ... }
//     func ExampleT_M() { ... }
//
// Multiple example functions for a package/type/function/method may be provided by
// appending a distinct suffix to the name. The suffix must start with a
// lower-case letter.
//
//     func Example_suffix() { ... }
//     func ExampleF_suffix() { ... }
//     func ExampleT_suffix() { ... }
//     func ExampleT_M_suffix() { ... }
//
// The entire test file is presented as the example when it contains a single
// example function, at least one other function, type, variable, or constant
// declaration, and no test or benchmark functions.
//
// Fuzzing
//
// Functions of the form
//     func FuzzXxx(*testing.F)
// are considered fuzz targets, and are executed by the "go test" command. When
// the -fuzz flag is provided, the functions will be fuzzed.
//
// For a description of the testing flags, see
// https://golang.org/cmd/go/#hdr-Testing_flags.
//
// For a description of fuzzing, see golang.org/s/draft-fuzzing-design.
//
// A sample fuzz target looks like this:
//     func FuzzBytesCmp(f *testing.F) {
//         f.Fuzz(func(t *testing.T, a, b []byte) {
//             if bytes.HasPrefix(a, b) && !bytes.Contains(a, b) {
//                 t.Error("HasPrefix is true, but Contains is false")
//             }
//         })
//     }
//
// Skipping
//
// Tests or benchmarks may be skipped at run time with a call to
// the Skip method of *T or *B:
//
//     func TestTimeConsuming(t *testing.T) {
//         if testing.Short() {
//             t.Skip("skipping test in short mode.")
//         }
//         ...
//     }
//
// The Skip method of *T can be used in a fuzz target if the input is invalid,
// but should not be considered a crash. For example:
//
//     func FuzzJSONMarshalling(f *testing.F) {
//         f.Fuzz(func(t *testing.T, b []byte) {
//             var v interface{}
//             if err := json.Unmarshal(b, &v); err != nil {
//                 t.Skip()
//             }
//             if _, err := json.Marshal(v); err != nil {
//                 t.Error("Marshal: %v", err)
//             }
//         })
//     }
//
// Subtests and Sub-benchmarks
//
// The Run methods of T and B allow defining subtests and sub-benchmarks,
// without having to define separate functions for each. This enables uses
// like table-driven benchmarks and creating hierarchical tests.
// It also provides a way to share common setup and tear-down code:
//
//     func TestFoo(t *testing.T) {
//         // <setup code>
//         t.Run("A=1", func(t *testing.T) { ... })
//         t.Run("A=2", func(t *testing.T) { ... })
//         t.Run("B=1", func(t *testing.T) { ... })
//         // <tear-down code>
//     }
//
// Each subtest and sub-benchmark has a unique name: the combination of the name
// of the top-level test and the sequence of names passed to Run, separated by
// slashes, with an optional trailing sequence number for disambiguation.
//
// The argument to the -run, -bench, and -fuzz command-line flags is an unanchored regular
// expression that matches the test's name. For tests with multiple slash-separated
// elements, such as subtests, the argument is itself slash-separated, with
// expressions matching each name element in turn. Because it is unanchored, an
// empty expression matches any string.
// For example, using "matching" to mean "whose name contains":
//
//     go test -run ''        # Run all tests.
//     go test -run Foo       # Run top-level tests matching "Foo", such as "TestFooBar".
//     go test -run Foo/A=    # For top-level tests matching "Foo", run subtests matching "A=".
//     go test -run /A=1      # For all top-level tests, run subtests matching "A=1".
//     go test -fuzz FuzzFoo  # Fuzz the target matching "FuzzFoo"
//
// The -run argument can also be used to run a specific value in the seed
// corpus, for debugging. For example:
//     go test -run=FuzzFoo/9ddb952d9814
//
// The -fuzz and -run flags can both be set, in order to fuzz a target but
// skip the execution of all other tests.
//
// Subtests can also be used to control parallelism. A parent test will only
// complete once all of its subtests complete. In this example, all tests are
// run in parallel with each other, and only with each other, regardless of
// other top-level tests that may be defined:
//
//     func TestGroupedParallel(t *testing.T) {
//         for _, tc := range tests {
//             tc := tc // capture range variable
//             t.Run(tc.Name, func(t *testing.T) {
//                 t.Parallel()
//                 ...
//             })
//         }
//     }
//
// The race detector kills the program if it exceeds 8128 concurrent goroutines,
// so use care when running parallel tests with the -race flag set.
//
// Run does not return until parallel subtests have completed, providing a way
// to clean up after a group of parallel tests:
//
//     func TestTeardownParallel(t *testing.T) {
//         // This Run will not return until the parallel tests finish.
//         t.Run("group", func(t *testing.T) {
//             t.Run("Test1", parallelTest1)
//             t.Run("Test2", parallelTest2)
//             t.Run("Test3", parallelTest3)
//         })
//         // <tear-down code>
//     }
//
// Main
//
// It is sometimes necessary for a test or benchmark program to do extra setup or teardown
// before or after it executes. It is also sometimes necessary to control
// which code runs on the main thread. To support these and other cases,
// if a test file contains a function:
//
//      func TestMain(m *testing.M)
//
// then the generated test will call TestMain(m) instead of running the tests or benchmarks
// directly. TestMain runs in the main goroutine and can do whatever setup
// and teardown is necessary around a call to m.Run. m.Run will return an exit
// code that may be passed to os.Exit. If TestMain returns, the test wrapper
// will pass the result of m.Run to os.Exit itself.
//
// When TestMain is called, flag.Parse has not been run. If TestMain depends on
// command-line flags, including those of the testing package, it should call
// flag.Parse explicitly. Command line flags are always parsed by the time test
// or benchmark functions run.
//
// A simple implementation of TestMain is:
//
//      func TestMain(m *testing.M) {
//              // call flag.Parse() here if TestMain uses flags
//              os.Exit(m.Run())
//      }
//
// TestMain is a low-level primitive and should not be necessary for casual
// testing needs, where ordinary test functions suffice.
package testing

import (
        "bytes"
        "errors"
        "flag"
        "fmt"
        "internal/race"
        "io"
        "math/rand"
        "os"
        "reflect"
        "runtime"
        "runtime/debug"
        "runtime/trace"
        "strconv"
        "strings"
        "sync"
        "sync/atomic"
        "time"
        "unicode"
        "unicode/utf8"
)

var initRan bool

// Init registers testing flags. These flags are automatically registered by
// the "go test" command before running test functions, so Init is only needed
// when calling functions such as Benchmark without using "go test".
//
// Init has no effect if it was already called.
func Init() {
        if initRan {
                return
        }
        initRan = true
        // The short flag requests that tests run more quickly, but its functionality
        // is provided by test writers themselves. The testing package is just its
        // home. The all.bash installation script sets it to make installation more
        // efficient, but by default the flag is off so a plain "go test" will do a
        // full test of the package.
        short = flag.Bool("test.short", false, "run smaller test suite to save time")

        // The failfast flag requests that test execution stop after the first test failure.
        failFast = flag.Bool("test.failfast", false, "do not start new tests after the first test failure")

        // The directory in which to create profile files and the like. When run from
        // "go test", the binary always runs in the source directory for the package;
        // this flag lets "go test" tell the binary to write the files in the directory where
        // the "go test" command is run.
        outputDir = flag.String("test.outputdir", "", "write profiles to `dir`")
        // Report as tests are run; default is silent for success.
        chatty = flag.Bool("test.v", false, "verbose: print additional output")
        count = flag.Uint("test.count", 1, "run tests and benchmarks `n` times")
        coverProfile = flag.String("test.coverprofile", "", "write a coverage profile to `file`")
        matchList = flag.String("test.list", "", "list tests, examples, and benchmarks matching `regexp` then exit")
        match = flag.String("test.run", "", "run only tests and examples matching `regexp`")
        memProfile = flag.String("test.memprofile", "", "write an allocation profile to `file`")
        memProfileRate = flag.Int("test.memprofilerate", 0, "set memory allocation profiling `rate` (see runtime.MemProfileRate)")
        cpuProfile = flag.String("test.cpuprofile", "", "write a cpu profile to `file`")
        blockProfile = flag.String("test.blockprofile", "", "write a goroutine blocking profile to `file`")
        blockProfileRate = flag.Int("test.blockprofilerate", 1, "set blocking profile `rate` (see runtime.SetBlockProfileRate)")
        mutexProfile = flag.String("test.mutexprofile", "", "write a mutex contention profile to the named file after execution")
        mutexProfileFraction = flag.Int("test.mutexprofilefraction", 1, "if >= 0, calls runtime.SetMutexProfileFraction()")
        panicOnExit0 = flag.Bool("test.paniconexit0", false, "panic on call to os.Exit(0)")
        traceFile = flag.String("test.trace", "", "write an execution trace to `file`")
        timeout = flag.Duration("test.timeout", 0, "panic test binary after duration `d` (default 0, timeout disabled)")
        cpuListStr = flag.String("test.cpu", "", "comma-separated `list` of cpu counts to run each test with")
        parallel = flag.Int("test.parallel", runtime.GOMAXPROCS(0), "run at most `n` tests in parallel")
        testlog = flag.String("test.testlogfile", "", "write test action log to `file` (for use only by cmd/go)")
        shuffle = flag.String("test.shuffle", "off", "randomize the execution order of tests and benchmarks")

        initBenchmarkFlags()
        initFuzzFlags()
}

var (
        // Flags, registered during Init.
        short                *bool
        failFast             *bool
        outputDir            *string
        chatty               *bool
        count                *uint
        coverProfile         *string
        matchList            *string
        match                *string
        memProfile           *string
        memProfileRate       *int
        cpuProfile           *string
        blockProfile         *string
        blockProfileRate     *int
        mutexProfile         *string
        mutexProfileFraction *int
        panicOnExit0         *bool
        traceFile            *string
        timeout              *time.Duration
        cpuListStr           *string
        parallel             *int
        shuffle              *string
        testlog              *string

        haveExamples bool // are there examples?

        cpuList     []int
        testlogFile *os.File

        numFailed uint32 // number of test failures
)

type chattyPrinter struct {
        w          io.Writer
        lastNameMu sync.Mutex // guards lastName
        lastName   string     // last printed test name in chatty mode
}

func newChattyPrinter(w io.Writer) *chattyPrinter {
        return &chattyPrinter{w: w}
}

// Updatef prints a message about the status of the named test to w.
//
// The formatted message must include the test name itself.
func (p *chattyPrinter) Updatef(testName, format string, args ...interface{}) {
        p.lastNameMu.Lock()
        defer p.lastNameMu.Unlock()

        // Since the message already implies an association with a specific new test,
        // we don't need to check what the old test name was or log an extra CONT line
        // for it. (We're updating it anyway, and the current message already includes
        // the test name.)
        p.lastName = testName
        fmt.Fprintf(p.w, format, args...)
}

// Printf prints a message, generated by the named test, that does not
// necessarily mention that tests's name itself.
func (p *chattyPrinter) Printf(testName, format string, args ...interface{}) {
        p.lastNameMu.Lock()
        defer p.lastNameMu.Unlock()

        if p.lastName == "" {
                p.lastName = testName
        } else if p.lastName != testName {
                fmt.Fprintf(p.w, "=== CONT  %s\n", testName)
                p.lastName = testName
        }

        fmt.Fprintf(p.w, format, args...)
}

// The maximum number of stack frames to go through when skipping helper functions for
// the purpose of decorating log messages.
const maxStackLen = 50

// common holds the elements common between T and B and
// captures common methods such as Errorf.
type common struct {
        mu          sync.RWMutex         // guards this group of fields
        output      []byte               // Output generated by test or benchmark.
        w           io.Writer            // For flushToParent.
        ran         bool                 // Test or benchmark (or one of its subtests) was executed.
        failed      bool                 // Test or benchmark has failed.
        skipped     bool                 // Test or benchmark has been skipped.
        done        bool                 // Test is finished and all subtests have completed.
        helperPCs   map[uintptr]struct{} // functions to be skipped when writing file/line info
        helperNames map[string]struct{}  // helperPCs converted to function names
        cleanups    []func()             // optional functions to be called at the end of the test
        cleanupName string               // Name of the cleanup function.
        cleanupPc   []uintptr            // The stack trace at the point where Cleanup was called.
        finished    bool                 // Test function has completed.

        chatty     *chattyPrinter // A copy of chattyPrinter, if the chatty flag is set.
        bench      bool           // Whether the current test is a benchmark.
        fuzzing    bool           // Whether the current test is a fuzzing target.
        hasSub     int32          // Written atomically.
        raceErrors int            // Number of races detected during test.
        runner     string         // Function name of tRunner running the test.

        parent   *common
        level    int       // Nesting depth of test or benchmark.
        creator  []uintptr // If level > 0, the stack trace at the point where the parent called t.Run.
        name     string    // Name of test or benchmark.
        start    time.Time // Time test or benchmark started
        duration time.Duration
        barrier  chan bool // To signal parallel subtests they may start.
        signal   chan bool // To signal a test is done.
        sub      []*T      // Queue of subtests to be run in parallel.

        tempDirMu  sync.Mutex
        tempDir    string
        tempDirErr error
        tempDirSeq int32
}

// Short reports whether the -test.short flag is set.
func Short() bool {
        if short == nil {
                panic("testing: Short called before Init")
        }
        // Catch code that calls this from TestMain without first calling flag.Parse.
        if !flag.Parsed() {
                panic("testing: Short called before Parse")
        }

        return *short
}

// CoverMode reports what the test coverage mode is set to. The
// values are "set", "count", or "atomic". The return value will be
// empty if test coverage is not enabled.
func CoverMode() string {
        return cover.Mode
}

// Verbose reports whether the -test.v flag is set.
func Verbose() bool {
        // Same as in Short.
        if chatty == nil {
                panic("testing: Verbose called before Init")
        }
        if !flag.Parsed() {
                panic("testing: Verbose called before Parse")
        }
        return *chatty
}

// frameSkip searches, starting after skip frames, for the first caller frame
// in a function not marked as a helper and returns that frame.
// The search stops if it finds a tRunner function that
// was the entry point into the test and the test is not a subtest.
// This function must be called with c.mu held.
func (c *common) frameSkip(skip int) runtime.Frame {
        // If the search continues into the parent test, we'll have to hold
        // its mu temporarily. If we then return, we need to unlock it.
        shouldUnlock := false
        defer func() {
                if shouldUnlock {
                        c.mu.Unlock()
                }
        }()
        var pc [maxStackLen]uintptr
        // Skip two extra frames to account for this function
        // and runtime.Callers itself.
        n := runtime.Callers(skip+2, pc[:])
        if n == 0 {
                panic("testing: zero callers found")
        }
        frames := runtime.CallersFrames(pc[:n])
        var firstFrame, prevFrame, frame runtime.Frame
        for more := true; more; prevFrame = frame {
                frame, more = frames.Next()
                if frame.Function == c.cleanupName {
                        frames = runtime.CallersFrames(c.cleanupPc)
                        continue
                }
                if firstFrame.PC == 0 {
                        firstFrame = frame
                }
                if frame.Function == c.runner {
                        // We've gone up all the way to the tRunner calling
                        // the test function (so the user must have
                        // called tb.Helper from inside that test function).
                        // If this is a top-level test, only skip up to the test function itself.
                        // If we're in a subtest, continue searching in the parent test,
                        // starting from the point of the call to Run which created this subtest.
                        if c.level > 1 {
                                frames = runtime.CallersFrames(c.creator)
                                parent := c.parent
                                // We're no longer looking at the current c after this point,
                                // so we should unlock its mu, unless it's the original receiver,
                                // in which case our caller doesn't expect us to do that.
                                if shouldUnlock {
                                        c.mu.Unlock()
                                }
                                c = parent
                                // Remember to unlock c.mu when we no longer need it, either
                                // because we went up another nesting level, or because we
                                // returned.
                                shouldUnlock = true
                                c.mu.Lock()
                                continue
                        }
                        return prevFrame
                }
                // If more helper PCs have been added since we last did the conversion
                if c.helperNames == nil {
                        c.helperNames = make(map[string]struct{})
                        for pc := range c.helperPCs {
                                c.helperNames[pcToName(pc)] = struct{}{}
                        }
                }
                if _, ok := c.helperNames[frame.Function]; !ok {
                        // Found a frame that wasn't inside a helper function.
                        return frame
                }
        }
        return firstFrame
}

// decorate prefixes the string with the file and line of the call site
// and inserts the final newline if needed and indentation spaces for formatting.
// This function must be called with c.mu held.
func (c *common) decorate(s string, skip int) string {
        // TODO(jayconrod,katiehockman): Consider refactoring the logging logic.
        // If more helper PCs have been added since we last did the conversion
        if c.helperNames == nil {
                c.helperNames = make(map[string]struct{})
                for pc := range c.helperPCs {
                        c.helperNames[pcToName(pc)] = struct{}{}
                }
        }

        frame := c.frameSkip(skip)
        file := frame.File
        line := frame.Line
        if file != "" {
                // Truncate file name at last file name separator.
                if index := strings.LastIndex(file, "/"); index >= 0 {
                        file = file[index+1:]
                } else if index = strings.LastIndex(file, "\\"); index >= 0 {
                        file = file[index+1:]
                }
        } else {
                file = "???"
        }
        if line == 0 {
                line = 1
        }
        buf := new(strings.Builder)
        // Every line is indented at least 4 spaces.
        buf.WriteString("    ")
        fmt.Fprintf(buf, "%s:%d: ", file, line)
        lines := strings.Split(s, "\n")
        if l := len(lines); l > 1 && lines[l-1] == "" {
                lines = lines[:l-1]
        }
        for i, line := range lines {
                if i > 0 {
                        // Second and subsequent lines are indented an additional 4 spaces.
                        buf.WriteString("\n        ")
                }
                buf.WriteString(line)
        }
        buf.WriteByte('\n')
        return buf.String()
}

// flushToParent writes c.output to the parent after first writing the header
// with the given format and arguments.
func (c *common) flushToParent(testName, format string, args ...interface{}) {
        p := c.parent
        p.mu.Lock()
        defer p.mu.Unlock()

        c.mu.Lock()
        defer c.mu.Unlock()

        if len(c.output) > 0 {
                format += "%s"
                args = append(args[:len(args):len(args)], c.output)
                c.output = c.output[:0] // but why?
        }

        if c.chatty != nil && p.w == c.chatty.w {
                // We're flushing to the actual output, so track that this output is
                // associated with a specific test (and, specifically, that the next output
                // is *not* associated with that test).
                //
                // Moreover, if c.output is non-empty it is important that this write be
                // atomic with respect to the output of other tests, so that we don't end up
                // with confusing '=== CONT' lines in the middle of our '--- PASS' block.
                // Neither humans nor cmd/test2json can parse those easily.
                // (See https://golang.org/issue/40771.)
                c.chatty.Updatef(testName, format, args...)
        } else {
                // We're flushing to the output buffer of the parent test, which will
                // itself follow a test-name header when it is finally flushed to stdout.
                fmt.Fprintf(p.w, format, args...)
        }
}

// isFuzzing returns whether the current context, or any of the parent contexts,
// are a fuzzing target
func (c *common) isFuzzing() bool {
        if c.fuzzing {
                return true
        }
        for parent := c.parent; parent != nil; parent = parent.parent {
                if parent.fuzzing {
                        return true
                }
        }
        return false
}

type indenter struct {
        c *common
}

func (w indenter) Write(b []byte) (n int, err error) {
        n = len(b)
        for len(b) > 0 {
                end := bytes.IndexByte(b, '\n')
                if end == -1 {
                        end = len(b)
                } else {
                        end++
                }
                // An indent of 4 spaces will neatly align the dashes with the status
                // indicator of the parent.
                const indent = "    "
                w.c.output = append(w.c.output, indent...)
                w.c.output = append(w.c.output, b[:end]...)
                b = b[end:]
        }
        return
}

// fmtDuration returns a string representing d in the form "87.00s".
func fmtDuration(d time.Duration) string {
        return fmt.Sprintf("%.2fs", d.Seconds())
}

// TB is the interface common to T and B.
type TB interface {
        Cleanup(func())
        Error(args ...interface{})
        Errorf(format string, args ...interface{})
        Fail()
        FailNow()
        Failed() bool
        Fatal(args ...interface{})
        Fatalf(format string, args ...interface{})
        Helper()
        Log(args ...interface{})
        Logf(format string, args ...interface{})
        Name() string
        Setenv(key, value string)
        Skip(args ...interface{})
        SkipNow()
        Skipf(format string, args ...interface{})
        Skipped() bool
        TempDir() string

        // A private method to prevent users implementing the
        // interface and so future additions to it will not
        // violate Go 1 compatibility.
        private()
}

var _ TB = (*T)(nil)
var _ TB = (*B)(nil)

// T is a type passed to Test functions to manage test state and support formatted test logs.
//
// A test ends when its Test function returns or calls any of the methods
// FailNow, Fatal, Fatalf, SkipNow, Skip, or Skipf. Those methods, as well as
// the Parallel method, must be called only from the goroutine running the
// Test function.
//
// The other reporting methods, such as the variations of Log and Error,
// may be called simultaneously from multiple goroutines.
type T struct {
        common
        isParallel bool
        isEnvSet   bool
        context    *testContext // For running tests and subtests.
}

func (c *common) private() {}

// Name returns the name of the running (sub-) test or benchmark.
//
// The name will include the name of the test along with the names of
// any nested sub-tests. If two sibling sub-tests have the same name,
// Name will append a suffix to guarantee the returned name is unique.
func (c *common) Name() string {
        return c.name
}

func (c *common) setRan() {
        if c.parent != nil {
                c.parent.setRan()
        }
        c.mu.Lock()
        defer c.mu.Unlock()
        c.ran = true
}

// Fail marks the function as having failed but continues execution.
func (c *common) Fail() {
        if c.parent != nil {
                c.parent.Fail()
        }
        c.mu.Lock()
        defer c.mu.Unlock()
        // c.done needs to be locked to synchronize checks to c.done in parent tests.
        if c.done {
                panic("Fail in goroutine after " + c.name + " has completed")
        }
        c.failed = true
}

// Failed reports whether the function has failed.
func (c *common) Failed() bool {
        c.mu.RLock()
        failed := c.failed
        c.mu.RUnlock()
        return failed || c.raceErrors+race.Errors() > 0
}

// FailNow marks the function as having failed and stops its execution
// by calling runtime.Goexit (which then runs all deferred calls in the
// current goroutine).
// Execution will continue at the next test or benchmark.
// FailNow must be called from the goroutine running the
// test or benchmark function, not from other goroutines
// created during the test. Calling FailNow does not stop
// those other goroutines.
func (c *common) FailNow() {
        c.Fail()

        // Calling runtime.Goexit will exit the goroutine, which
        // will run the deferred functions in this goroutine,
        // which will eventually run the deferred lines in tRunner,
        // which will signal to the test loop that this test is done.
        //
        // A previous version of this code said:
        //
        //      c.duration = ...
        //      c.signal <- c.self
        //      runtime.Goexit()
        //
        // This previous version duplicated code (those lines are in
        // tRunner no matter what), but worse the goroutine teardown
        // implicit in runtime.Goexit was not guaranteed to complete
        // before the test exited. If a test deferred an important cleanup
        // function (like removing temporary files), there was no guarantee
        // it would run on a test failure. Because we send on c.signal during
        // a top-of-stack deferred function now, we know that the send
        // only happens after any other stacked defers have completed.
        c.mu.Lock()
        c.finished = true
        c.mu.Unlock()
        runtime.Goexit()
}

// log generates the output. It's always at the same stack depth.
func (c *common) log(s string) {
        c.logDepth(s, 3) // logDepth + log + public function
}

// logDepth generates the output at an arbitrary stack depth.
func (c *common) logDepth(s string, depth int) {
        c.mu.Lock()
        defer c.mu.Unlock()
        if c.done {
                // This test has already finished. Try and log this message
                // with our parent. If we don't have a parent, panic.
                for parent := c.parent; parent != nil; parent = parent.parent {
                        parent.mu.Lock()
                        defer parent.mu.Unlock()
                        if !parent.done {
                                parent.output = append(parent.output, parent.decorate(s, depth+1)...)
                                return
                        }
                }
                panic("Log in goroutine after " + c.name + " has completed: " + s)
        } else {
                if c.chatty != nil {
                        if c.bench {
                                // Benchmarks don't print === CONT, so we should skip the test
                                // printer and just print straight to stdout.
                                fmt.Print(c.decorate(s, depth+1))
                        } else {
                                c.chatty.Printf(c.name, "%s", c.decorate(s, depth+1))
                        }

                        return
                }
                c.output = append(c.output, c.decorate(s, depth+1)...)
        }
}

// Log formats its arguments using default formatting, analogous to Println,
// and records the text in the error log. For tests, the text will be printed only if
// the test fails or the -test.v flag is set. For benchmarks, the text is always
// printed to avoid having performance depend on the value of the -test.v flag.
func (c *common) Log(args ...interface{}) { c.log(fmt.Sprintln(args...)) }

// Logf formats its arguments according to the format, analogous to Printf, and
// records the text in the error log. A final newline is added if not provided. For
// tests, the text will be printed only if the test fails or the -test.v flag is
// set. For benchmarks, the text is always printed to avoid having performance
// depend on the value of the -test.v flag.
func (c *common) Logf(format string, args ...interface{}) { c.log(fmt.Sprintf(format, args...)) }

// Error is equivalent to Log followed by Fail.
func (c *common) Error(args ...interface{}) {
        c.log(fmt.Sprintln(args...))
        c.Fail()
}

// Errorf is equivalent to Logf followed by Fail.
func (c *common) Errorf(format string, args ...interface{}) {
        c.log(fmt.Sprintf(format, args...))
        c.Fail()
}

// Fatal is equivalent to Log followed by FailNow.
func (c *common) Fatal(args ...interface{}) {
        c.log(fmt.Sprintln(args...))
        c.FailNow()
}

// Fatalf is equivalent to Logf followed by FailNow.
func (c *common) Fatalf(format string, args ...interface{}) {
        c.log(fmt.Sprintf(format, args...))
        c.FailNow()
}

// Skip is equivalent to Log followed by SkipNow.
func (c *common) Skip(args ...interface{}) {
        c.log(fmt.Sprintln(args...))
        c.SkipNow()
}

// Skipf is equivalent to Logf followed by SkipNow.
func (c *common) Skipf(format string, args ...interface{}) {
        c.log(fmt.Sprintf(format, args...))
        c.SkipNow()
}

// SkipNow marks the test as having been skipped and stops its execution
// by calling runtime.Goexit.
// If a test fails (see Error, Errorf, Fail) and is then skipped,
// it is still considered to have failed.
// Execution will continue at the next test or benchmark. See also FailNow.
// SkipNow must be called from the goroutine running the test, not from
// other goroutines created during the test. Calling SkipNow does not stop
// those other goroutines.
func (c *common) SkipNow() {
        c.mu.Lock()
        c.skipped = true
        c.finished = true
        c.mu.Unlock()
        runtime.Goexit()
}

// Skipped reports whether the test was skipped.
func (c *common) Skipped() bool {
        c.mu.RLock()
        defer c.mu.RUnlock()
        return c.skipped
}

// Helper marks the calling function as a test helper function.
// When printing file and line information, that function will be skipped.
// Helper may be called simultaneously from multiple goroutines.
func (c *common) Helper() {
        c.mu.Lock()
        defer c.mu.Unlock()
        if c.helperPCs == nil {
                c.helperPCs = make(map[uintptr]struct{})
        }
        // repeating code from callerName here to save walking a stack frame
        var pc [1]uintptr
        n := runtime.Callers(2, pc[:]) // skip runtime.Callers + Helper
        if n == 0 {
                panic("testing: zero callers found")
        }
        if _, found := c.helperPCs[pc[0]]; !found {
                c.helperPCs[pc[0]] = struct{}{}
                c.helperNames = nil // map will be recreated next time it is needed
        }
}

// Cleanup registers a function to be called when the test (or subtest) and all its
// subtests complete. Cleanup functions will be called in last added,
// first called order.
func (c *common) Cleanup(f func()) {
        var pc [maxStackLen]uintptr
        // Skip two extra frames to account for this function and runtime.Callers itself.
        n := runtime.Callers(2, pc[:])
        cleanupPc := pc[:n]

        fn := func() {
                defer func() {
                        c.mu.Lock()
                        defer c.mu.Unlock()
                        c.cleanupName = ""
                        c.cleanupPc = nil
                }()

                name := callerName(0)
                c.mu.Lock()
                c.cleanupName = name
                c.cleanupPc = cleanupPc
                c.mu.Unlock()

                f()
        }

        c.mu.Lock()
        defer c.mu.Unlock()
        c.cleanups = append(c.cleanups, fn)
}

// TempDir returns a temporary directory for the test to use.
// The directory is automatically removed by Cleanup when the test and
// all its subtests complete.
// Each subsequent call to t.TempDir returns a unique directory;
// if the directory creation fails, TempDir terminates the test by calling Fatal.
func (c *common) TempDir() string {
        // Use a single parent directory for all the temporary directories
        // created by a test, each numbered sequentially.
        c.tempDirMu.Lock()
        var nonExistent bool
        if c.tempDir == "" { // Usually the case with js/wasm
                nonExistent = true
        } else {
                _, err := os.Stat(c.tempDir)
                nonExistent = os.IsNotExist(err)
                if err != nil && !nonExistent {
                        c.Fatalf("TempDir: %v", err)
                }
        }

        if nonExistent {
                c.Helper()

                // Drop unusual characters (such as path separators or
                // characters interacting with globs) from the directory name to
                // avoid surprising os.MkdirTemp behavior.
                mapper := func(r rune) rune {
                        if r < utf8.RuneSelf {
                                const allowed = "!#$%&()+,-.=@^_{}~ "
                                if '0' <= r && r <= '9' ||
                                        'a' <= r && r <= 'z' ||
                                        'A' <= r && r <= 'Z' {
                                        return r
                                }
                                if strings.ContainsRune(allowed, r) {
                                        return r
                                }
                        } else if unicode.IsLetter(r) || unicode.IsNumber(r) {
                                return r
                        }
                        return -1
                }
                pattern := strings.Map(mapper, c.Name())
                c.tempDir, c.tempDirErr = os.MkdirTemp("", pattern)
                if c.tempDirErr == nil {
                        c.Cleanup(func() {
                                if err := os.RemoveAll(c.tempDir); err != nil {
                                        c.Errorf("TempDir RemoveAll cleanup: %v", err)
                                }
                        })
                }
        }
        c.tempDirMu.Unlock()

        if c.tempDirErr != nil {
                c.Fatalf("TempDir: %v", c.tempDirErr)
        }
        seq := atomic.AddInt32(&c.tempDirSeq, 1)
        dir := fmt.Sprintf("%s%c%03d", c.tempDir, os.PathSeparator, seq)
        if err := os.Mkdir(dir, 0777); err != nil {
                c.Fatalf("TempDir: %v", err)
        }
        return dir
}

// Setenv calls os.Setenv(key, value) and uses Cleanup to
// restore the environment variable to its original value
// after the test.
//
// This cannot be used in parallel tests.
func (c *common) Setenv(key, value string) {
        prevValue, ok := os.LookupEnv(key)

        if err := os.Setenv(key, value); err != nil {
                c.Fatalf("cannot set environment variable: %v", err)
        }

        if ok {
                c.Cleanup(func() {
                        os.Setenv(key, prevValue)
                })
        } else {
                c.Cleanup(func() {
                        os.Unsetenv(key)
                })
        }
}

// panicHanding is an argument to runCleanup.
type panicHandling int

const (
        normalPanic panicHandling = iota
        recoverAndReturnPanic
)

// runCleanup is called at the end of the test.
// If catchPanic is true, this will catch panics, and return the recovered
// value if any.
func (c *common) runCleanup(ph panicHandling) (panicVal interface{}) {
        if ph == recoverAndReturnPanic {
                defer func() {
                        panicVal = recover()
                }()
        }

        // Make sure that if a cleanup function panics,
        // we still run the remaining cleanup functions.
        defer func() {
                c.mu.Lock()
                recur := len(c.cleanups) > 0
                c.mu.Unlock()
                if recur {
                        c.runCleanup(normalPanic)
                }
        }()

        for {
                var cleanup func()
                c.mu.Lock()
                if len(c.cleanups) > 0 {
                        last := len(c.cleanups) - 1
                        cleanup = c.cleanups[last]
                        c.cleanups = c.cleanups[:last]
                }
                c.mu.Unlock()
                if cleanup == nil {
                        return nil
                }
                cleanup()
        }
}

// callerName gives the function name (qualified with a package path)
// for the caller after skip frames (where 0 means the current function).
func callerName(skip int) string {
        var pc [1]uintptr
        n := runtime.Callers(skip+2, pc[:]) // skip + runtime.Callers + callerName
        if n == 0 {
                panic("testing: zero callers found")
        }
        return pcToName(pc[0])
}

func pcToName(pc uintptr) string {
        pcs := []uintptr{pc}
        frames := runtime.CallersFrames(pcs)
        frame, _ := frames.Next()
        return frame.Function
}

// Parallel signals that this test is to be run in parallel with (and only with)
// other parallel tests. When a test is run multiple times due to use of
// -test.count or -test.cpu, multiple instances of a single test never run in
// parallel with each other.
func (t *T) Parallel() {
        if t.isParallel {
                panic("testing: t.Parallel called multiple times")
        }
        if t.isEnvSet {
                panic("testing: t.Parallel called after t.Setenv; cannot set environment variables in parallel tests")
        }
        t.isParallel = true
        if t.parent.barrier == nil {
                // T.Parallel has no effect when fuzzing.
                // Multiple processes may run in parallel, but only one input can run at a
                // time per process so we can attribute crashes to specific inputs.
                return
        }

        // We don't want to include the time we spend waiting for serial tests
        // in the test duration. Record the elapsed time thus far and reset the
        // timer afterwards.
        t.duration += time.Since(t.start)

        // Add to the list of tests to be released by the parent.
        t.parent.sub = append(t.parent.sub, t)
        t.raceErrors += race.Errors()

        if t.chatty != nil {
                // Unfortunately, even though PAUSE indicates that the named test is *no
                // longer* running, cmd/test2json interprets it as changing the active test
                // for the purpose of log parsing. We could fix cmd/test2json, but that
                // won't fix existing deployments of third-party tools that already shell
                // out to older builds of cmd/test2json — so merely fixing cmd/test2json
                // isn't enough for now.
                t.chatty.Updatef(t.name, "=== PAUSE %s\n", t.name)
        }

        t.signal <- true   // Release calling test.
        <-t.parent.barrier // Wait for the parent test to complete.
        t.context.waitParallel()

        if t.chatty != nil {
                t.chatty.Updatef(t.name, "=== CONT  %s\n", t.name)
        }

        t.start = time.Now()
        t.raceErrors += -race.Errors()
}

// Setenv calls os.Setenv(key, value) and uses Cleanup to
// restore the environment variable to its original value
// after the test.
//
// This cannot be used in parallel tests.
func (t *T) Setenv(key, value string) {
        if t.isParallel {
                panic("testing: t.Setenv called after t.Parallel; cannot set environment variables in parallel tests")
        }

        t.isEnvSet = true

        t.common.Setenv(key, value)
}

// InternalTest is an internal type but exported because it is cross-package;
// it is part of the implementation of the "go test" command.
type InternalTest struct {
        Name string
        F    func(*T)
}

var errNilPanicOrGoexit = errors.New("test executed panic(nil) or runtime.Goexit")

func tRunner(t *T, fn func(t *T)) {
        t.runner = callerName(0)

        // When this goroutine is done, either because fn(t)
        // returned normally or because a test failure triggered
        // a call to runtime.Goexit, record the duration and send
        // a signal saying that the test is done.
        defer func() {
                if t.Failed() {
                        atomic.AddUint32(&numFailed, 1)
                }

                if t.raceErrors+race.Errors() > 0 {
                        t.Errorf("race detected during execution of test")
                }

                // If the test panicked, print any test output before dying.
                err := recover()
                signal := true

                t.mu.RLock()
                finished := t.finished
                t.mu.RUnlock()
                if !finished && err == nil {
                        err = errNilPanicOrGoexit
                        for p := t.parent; p != nil; p = p.parent {
                                p.mu.RLock()
                                finished = p.finished
                                p.mu.RUnlock()
                                if finished {
                                        t.Errorf("%v: subtest may have called FailNow on a parent test", err)
                                        err = nil
                                        signal = false
                                        break
                                }
                        }
                }
                // Use a deferred call to ensure that we report that the test is
                // complete even if a cleanup function calls t.FailNow. See issue 41355.
                didPanic := false
                defer func() {
                        isFuzzing := t.common.isFuzzing()
                        if didPanic && !isFuzzing {
                                return
                        }
                        if err != nil && !isFuzzing {
                                panic(err)
                        }
                        // Only report that the test is complete if it doesn't panic,
                        // as otherwise the test binary can exit before the panic is
                        // reported to the user. See issue 41479.
                        t.signal <- signal
                }()

                doPanic := func(err interface{}) {
                        t.Fail()
                        if r := t.runCleanup(recoverAndReturnPanic); r != nil {
                                t.Logf("cleanup panicked with %v", r)
                        }
                        // Flush the output log up to the root before dying.
                        for root := &t.common; root.parent != nil; root = root.parent {
                                root.mu.Lock()
                                root.duration += time.Since(root.start)
                                d := root.duration
                                root.mu.Unlock()
                                root.flushToParent(root.name, "--- FAIL: %s (%s)\n", root.name, fmtDuration(d))
                                if r := root.parent.runCleanup(recoverAndReturnPanic); r != nil {
                                        fmt.Fprintf(root.parent.w, "cleanup panicked with %v", r)
                                }
                        }
                        didPanic = true
                        if t.common.fuzzing {
                                for root := &t.common; root.parent != nil; root = root.parent {
                                        fmt.Fprintf(root.parent.w, "panic: %s\n%s\n", err, string(debug.Stack()))
                                }
                                return
                        }
                        panic(err)
                }
                if err != nil {
                        doPanic(err)
                }

                t.duration += time.Since(t.start)

                if len(t.sub) > 0 {
                        // Run parallel subtests.
                        // Decrease the running count for this test.
                        t.context.release()
                        // Release the parallel subtests.
                        close(t.barrier)
                        // Wait for subtests to complete.
                        for _, sub := range t.sub {
                                <-sub.signal
                        }
                        cleanupStart := time.Now()
                        err := t.runCleanup(recoverAndReturnPanic)
                        t.duration += time.Since(cleanupStart)
                        if err != nil {
                                doPanic(err)
                        }
                        if !t.isParallel {
                                // Reacquire the count for sequential tests. See comment in Run.
                                t.context.waitParallel()
                        }
                } else if t.isParallel {
                        // Only release the count for this test if it was run as a parallel
                        // test. See comment in Run method.
                        t.context.release()
                }
                t.report() // Report after all subtests have finished.

                // Do not lock t.done to allow race detector to detect race in case
                // the user does not appropriately synchronizes a goroutine.
                t.done = true
                if t.parent != nil && atomic.LoadInt32(&t.hasSub) == 0 {
                        t.setRan()
                }
        }()
        defer func() {
                if len(t.sub) == 0 {
                        t.runCleanup(normalPanic)
                }
        }()

        t.start = time.Now()
        t.raceErrors = -race.Errors()
        fn(t)

        // code beyond here will not be executed when FailNow is invoked
        t.mu.Lock()
        t.finished = true
        t.mu.Unlock()
}

// Run runs f as a subtest of t called name. It runs f in a separate goroutine
// and blocks until f returns or calls t.Parallel to become a parallel test.
// Run reports whether f succeeded (or at least did not fail before calling t.Parallel).
//
// Run may be called simultaneously from multiple goroutines, but all such calls
// must return before the outer test function for t returns.
func (t *T) Run(name string, f func(t *T)) bool {
        atomic.StoreInt32(&t.hasSub, 1)
        testName, ok, _ := t.context.match.fullName(&t.common, name)
        if !ok || shouldFailFast() {
                return true
        }
        // Record the stack trace at the point of this call so that if the subtest
        // function - which runs in a separate stack - is marked as a helper, we can
        // continue walking the stack into the parent test.
        var pc [maxStackLen]uintptr
        n := runtime.Callers(2, pc[:])
        t = &T{
                common: common{
                        barrier: make(chan bool),
                        signal:  make(chan bool, 1),
                        name:    testName,
                        parent:  &t.common,
                        level:   t.level + 1,
                        creator: pc[:n],
                        chatty:  t.chatty,
                },
                context: t.context,
        }
        t.w = indenter{&t.common}

        if t.chatty != nil {
                t.chatty.Updatef(t.name, "=== RUN   %s\n", t.name)
        }
        // Instead of reducing the running count of this test before calling the
        // tRunner and increasing it afterwards, we rely on tRunner keeping the
        // count correct. This ensures that a sequence of sequential tests runs
        // without being preempted, even when their parent is a parallel test. This
        // may especially reduce surprises if *parallel == 1.
        go tRunner(t, f)
        if !<-t.signal {
                // At this point, it is likely that FailNow was called on one of the
                // parent tests by one of the subtests. Continue aborting up the chain.
                runtime.Goexit()
        }
        return !t.failed
}

// Deadline reports the time at which the test binary will have
// exceeded the timeout specified by the -timeout flag.
//
// The ok result is false if the -timeout flag indicates “no timeout” (0).
func (t *T) Deadline() (deadline time.Time, ok bool) {
        deadline = t.context.deadline
        return deadline, !deadline.IsZero()
}

// testContext holds all fields that are common to all tests. This includes
// synchronization primitives to run at most *parallel tests.
type testContext struct {
        match    *matcher
        deadline time.Time

        mu sync.Mutex

        // Channel used to signal tests that are ready to be run in parallel.
        startParallel chan bool

        // running is the number of tests currently running in parallel.
        // This does not include tests that are waiting for subtests to complete.
        running int

        // numWaiting is the number tests waiting to be run in parallel.
        numWaiting int

        // maxParallel is a copy of the parallel flag.
        maxParallel int
}

func newTestContext(maxParallel int, m *matcher) *testContext {
        return &testContext{
                match:         m,
                startParallel: make(chan bool),
                maxParallel:   maxParallel,
                running:       1, // Set the count to 1 for the main (sequential) test.
        }
}

func (c *testContext) waitParallel() {
        c.mu.Lock()
        if c.running < c.maxParallel {
                c.running++
                c.mu.Unlock()
                return
        }
        c.numWaiting++
        c.mu.Unlock()
        <-c.startParallel
}

func (c *testContext) release() {
        c.mu.Lock()
        if c.numWaiting == 0 {
                c.running--
                c.mu.Unlock()
                return
        }
        c.numWaiting--
        c.mu.Unlock()
        c.startParallel <- true // Pick a waiting test to be run.
}

// No one should be using func Main anymore.
// See the doc comment on func Main and use MainStart instead.
var errMain = errors.New("testing: unexpected use of func Main")

type matchStringOnly func(pat, str string) (bool, error)

func (f matchStringOnly) MatchString(pat, str string) (bool, error)   { return f(pat, str) }
func (f matchStringOnly) StartCPUProfile(w io.Writer) error           { return errMain }
func (f matchStringOnly) StopCPUProfile()                             {}
func (f matchStringOnly) WriteProfileTo(string, io.Writer, int) error { return errMain }
func (f matchStringOnly) ImportPath() string                          { return "" }
func (f matchStringOnly) StartTestLog(io.Writer)                      {}
func (f matchStringOnly) StopTestLog() error                          { return errMain }
func (f matchStringOnly) SetPanicOnExit0(bool)                        {}
func (f matchStringOnly) CoordinateFuzzing(time.Duration, int64, time.Duration, int64, int, []corpusEntry, []reflect.Type, string, string) error {
        return errMain
}
func (f matchStringOnly) RunFuzzWorker(func(corpusEntry) error) error { return errMain }
func (f matchStringOnly) ReadCorpus(string, []reflect.Type) ([]corpusEntry, error) {
        return nil, errMain
}
func (f matchStringOnly) CheckCorpus([]interface{}, []reflect.Type) error { return nil }
func (f matchStringOnly) ResetCoverage()                                  {}
func (f matchStringOnly) SnapshotCoverage()                               {}

// Main is an internal function, part of the implementation of the "go test" command.
// It was exported because it is cross-package and predates "internal" packages.
// It is no longer used by "go test" but preserved, as much as possible, for other
// systems that simulate "go test" using Main, but Main sometimes cannot be updated as
// new functionality is added to the testing package.
// Systems simulating "go test" should be updated to use MainStart.
func Main(matchString func(pat, str string) (bool, error), tests []InternalTest, benchmarks []InternalBenchmark, examples []InternalExample) {
        os.Exit(MainStart(matchStringOnly(matchString), tests, benchmarks, nil, examples).Run())
}

// M is a type passed to a TestMain function to run the actual tests.
type M struct {
        deps        testDeps
        tests       []InternalTest
        benchmarks  []InternalBenchmark
        fuzzTargets []InternalFuzzTarget
        examples    []InternalExample

        timer     *time.Timer
        afterOnce sync.Once

        numRun int

        // value to pass to os.Exit, the outer test func main
        // harness calls os.Exit with this code. See #34129.
        exitCode int
}

// testDeps is an internal interface of functionality that is
// passed into this package by a test's generated main package.
// The canonical implementation of this interface is
// testing/internal/testdeps's TestDeps.
type testDeps interface {
        ImportPath() string
        MatchString(pat, str string) (bool, error)
        SetPanicOnExit0(bool)
        StartCPUProfile(io.Writer) error
        StopCPUProfile()
        StartTestLog(io.Writer)
        StopTestLog() error
        WriteProfileTo(string, io.Writer, int) error
        CoordinateFuzzing(time.Duration, int64, time.Duration, int64, int, []corpusEntry, []reflect.Type, string, string) error
        RunFuzzWorker(func(corpusEntry) error) error
        ReadCorpus(string, []reflect.Type) ([]corpusEntry, error)
        CheckCorpus([]interface{}, []reflect.Type) error
        ResetCoverage()
        SnapshotCoverage()
}

// MainStart is meant for use by tests generated by 'go test'.
// It is not meant to be called directly and is not subject to the Go 1 compatibility document.
// It may change signature from release to release.
func MainStart(deps testDeps, tests []InternalTest, benchmarks []InternalBenchmark, fuzzTargets []InternalFuzzTarget, examples []InternalExample) *M {
        Init()
        return &M{
                deps:        deps,
                tests:       tests,
                benchmarks:  benchmarks,
                fuzzTargets: fuzzTargets,
                examples:    examples,
        }
}

// Run runs the tests. It returns an exit code to pass to os.Exit.
func (m *M) Run() (code int) {
        defer func() {
                code = m.exitCode
        }()

        // Count the number of calls to m.Run.
        // We only ever expected 1, but we didn't enforce that,
        // and now there are tests in the wild that call m.Run multiple times.
        // Sigh. golang.org/issue/23129.
        m.numRun++

        // TestMain may have already called flag.Parse.
        if !flag.Parsed() {
                flag.Parse()
        }

        if *parallel < 1 {
                fmt.Fprintln(os.Stderr, "testing: -parallel can only be given a positive integer")
                flag.Usage()
                m.exitCode = 2
                return
        }
        if *matchFuzz != "" && *fuzzCacheDir == "" {
                fmt.Fprintln(os.Stderr, "testing: internal error: -test.fuzzcachedir must be set if -test.fuzz is set")
                flag.Usage()
                m.exitCode = 2
                return
        }

        if len(*matchList) != 0 {
                listTests(m.deps.MatchString, m.tests, m.benchmarks, m.fuzzTargets, m.examples)
                m.exitCode = 0
                return
        }

        if *shuffle != "off" {
                var n int64
                var err error
                if *shuffle == "on" {
                        n = time.Now().UnixNano()
                } else {
                        n, err = strconv.ParseInt(*shuffle, 10, 64)
                        if err != nil {
                                fmt.Fprintln(os.Stderr, `testing: -shuffle should be "off", "on", or a valid integer:`, err)
                                m.exitCode = 2
                                return
                        }
                }
                fmt.Println("-test.shuffle", n)
                rng := rand.New(rand.NewSource(n))
                rng.Shuffle(len(m.tests), func(i, j int) { m.tests[i], m.tests[j] = m.tests[j], m.tests[i] })
                rng.Shuffle(len(m.benchmarks), func(i, j int) { m.benchmarks[i], m.benchmarks[j] = m.benchmarks[j], m.benchmarks[i] })
        }

        parseCpuList()

        m.before()
        defer m.after()
        if !*isFuzzWorker {
                // The fuzzing coordinator will already run all tests, examples,
                // and benchmarks. Don't make the workers do redundant work.
                deadline := m.startAlarm()
                haveExamples = len(m.examples) > 0
                testRan, testOk := runTests(m.deps.MatchString, m.tests, deadline)
                fuzzTargetsRan, fuzzTargetsOk := runFuzzTargets(m.deps, m.fuzzTargets, deadline)
                exampleRan, exampleOk := runExamples(m.deps.MatchString, m.examples)
                m.stopAlarm()
                if !testRan && !exampleRan && !fuzzTargetsRan && *matchBenchmarks == "" && *matchFuzz == "" {
                        fmt.Fprintln(os.Stderr, "testing: warning: no tests to run")
                }
                if !testOk || !exampleOk || !fuzzTargetsOk || !runBenchmarks(m.deps.ImportPath(), m.deps.MatchString, m.benchmarks) || race.Errors() > 0 {
                        fmt.Println("FAIL")
                        m.exitCode = 1
                        return
                }
        }

        fuzzingRan, fuzzingMatched, fuzzingOk := runFuzzing(m.deps, m.fuzzTargets)
        if *matchFuzz != "" && !fuzzingRan {
                if fuzzingMatched == 0 {
                        fmt.Fprintln(os.Stderr, "testing: warning: no targets to fuzz")
                } else {
                        fmt.Fprintln(os.Stderr, "testing: warning: will not fuzz, -fuzz matches more than one target")
                }
        }
        if !*isFuzzWorker && !fuzzingOk {
                fmt.Println("FAIL")
                if *isFuzzWorker {
                        m.exitCode = fuzzWorkerExitCode
                } else {
                        m.exitCode = 1
                }
                return
        }

        m.exitCode = 0
        if !*isFuzzWorker {
                fmt.Println("PASS")
        }
        return
}

func (t *T) report() {
        if t.parent == nil {
                return
        }
        dstr := fmtDuration(t.duration)
        format := "--- %s: %s (%s)\n"
        if t.Failed() {
                t.flushToParent(t.name, format, "FAIL", t.name, dstr)
        } else if t.chatty != nil {
                if t.Skipped() {
                        t.flushToParent(t.name, format, "SKIP", t.name, dstr)
                } else {
                        t.flushToParent(t.name, format, "PASS", t.name, dstr)
                }
        }
}

func listTests(matchString func(pat, str string) (bool, error), tests []InternalTest, benchmarks []InternalBenchmark, fuzzTargets []InternalFuzzTarget, examples []InternalExample) {
        if _, err := matchString(*matchList, "non-empty"); err != nil {
                fmt.Fprintf(os.Stderr, "testing: invalid regexp in -test.list (%q): %s\n", *matchList, err)
                os.Exit(1)
        }

        for _, test := range tests {
                if ok, _ := matchString(*matchList, test.Name); ok {
                        fmt.Println(test.Name)
                }
        }
        for _, bench := range benchmarks {
                if ok, _ := matchString(*matchList, bench.Name); ok {
                        fmt.Println(bench.Name)
                }
        }
        for _, fuzzTarget := range fuzzTargets {
                if ok, _ := matchString(*matchList, fuzzTarget.Name); ok {
                        fmt.Println(fuzzTarget.Name)
                }
        }
        for _, example := range examples {
                if ok, _ := matchString(*matchList, example.Name); ok {
                        fmt.Println(example.Name)
                }
        }
}

// RunTests is an internal function but exported because it is cross-package;
// it is part of the implementation of the "go test" command.
func RunTests(matchString func(pat, str string) (bool, error), tests []InternalTest) (ok bool) {
        var deadline time.Time
        if *timeout > 0 {
                deadline = time.Now().Add(*timeout)
        }
        ran, ok := runTests(matchString, tests, deadline)
        if !ran && !haveExamples {
                fmt.Fprintln(os.Stderr, "testing: warning: no tests to run")
        }
        return ok
}

func runTests(matchString func(pat, str string) (bool, error), tests []InternalTest, deadline time.Time) (ran, ok bool) {
        ok = true
        for _, procs := range cpuList {
                runtime.GOMAXPROCS(procs)
                for i := uint(0); i < *count; i++ {
                        if shouldFailFast() {
                                break
                        }
                        ctx := newTestContext(*parallel, newMatcher(matchString, *match, "-test.run"))
                        ctx.deadline = deadline
                        t := &T{
                                common: common{
                                        signal:  make(chan bool, 1),
                                        barrier: make(chan bool),
                                        w:       os.Stdout,
                                },
                                context: ctx,
                        }
                        if Verbose() {
                                t.chatty = newChattyPrinter(t.w)
                        }
                        tRunner(t, func(t *T) {
                                for _, test := range tests {
                                        t.Run(test.Name, test.F)
                                }
                        })
                        select {
                        case <-t.signal:
                        default:
                                panic("internal error: tRunner exited without sending on t.signal")
                        }
                        ok = ok && !t.Failed()
                        ran = ran || t.ran
                }
        }
        return ran, ok
}

// before runs before all testing.
func (m *M) before() {
        if *memProfileRate > 0 {
                runtime.MemProfileRate = *memProfileRate
        }
        if *cpuProfile != "" {
                f, err := os.Create(toOutputDir(*cpuProfile))
                if err != nil {
                        fmt.Fprintf(os.Stderr, "testing: %s\n", err)
                        return
                }
                if err := m.deps.StartCPUProfile(f); err != nil {
                        fmt.Fprintf(os.Stderr, "testing: can't start cpu profile: %s\n", err)
                        f.Close()
                        return
                }
                // Could save f so after can call f.Close; not worth the effort.
        }
        if *traceFile != "" {
                f, err := os.Create(toOutputDir(*traceFile))
                if err != nil {
                        fmt.Fprintf(os.Stderr, "testing: %s\n", err)
                        return
                }
                if err := trace.Start(f); err != nil {
                        fmt.Fprintf(os.Stderr, "testing: can't start tracing: %s\n", err)
                        f.Close()
                        return
                }
                // Could save f so after can call f.Close; not worth the effort.
        }
        if *blockProfile != "" && *blockProfileRate >= 0 {
                runtime.SetBlockProfileRate(*blockProfileRate)
        }
        if *mutexProfile != "" && *mutexProfileFraction >= 0 {
                runtime.SetMutexProfileFraction(*mutexProfileFraction)
        }
        if *coverProfile != "" && cover.Mode == "" {
                fmt.Fprintf(os.Stderr, "testing: cannot use -test.coverprofile because test binary was not built with coverage enabled\n")
                os.Exit(2)
        }
        if *testlog != "" {
                // Note: Not using toOutputDir.
                // This file is for use by cmd/go, not users.
                var f *os.File
                var err error
                if m.numRun == 1 {
                        f, err = os.Create(*testlog)
                } else {
                        f, err = os.OpenFile(*testlog, os.O_WRONLY, 0)
                        if err == nil {
                                f.Seek(0, io.SeekEnd)
                        }
                }
                if err != nil {
                        fmt.Fprintf(os.Stderr, "testing: %s\n", err)
                        os.Exit(2)
                }
                m.deps.StartTestLog(f)
                testlogFile = f
        }
        if *panicOnExit0 {
                m.deps.SetPanicOnExit0(true)
        }
}

// after runs after all testing.
func (m *M) after() {
        m.afterOnce.Do(func() {
                m.writeProfiles()
        })

        // Restore PanicOnExit0 after every run, because we set it to true before
        // every run. Otherwise, if m.Run is called multiple times the behavior of
        // os.Exit(0) will not be restored after the second run.
        if *panicOnExit0 {
                m.deps.SetPanicOnExit0(false)
        }
}

func (m *M) writeProfiles() {
        if *testlog != "" {
                if err := m.deps.StopTestLog(); err != nil {
                        fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *testlog, err)
                        os.Exit(2)
                }
                if err := testlogFile.Close(); err != nil {
                        fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *testlog, err)
                        os.Exit(2)
                }
        }
        if *cpuProfile != "" {
                m.deps.StopCPUProfile() // flushes profile to disk
        }
        if *traceFile != "" {
                trace.Stop() // flushes trace to disk
        }
        if *memProfile != "" {
                f, err := os.Create(toOutputDir(*memProfile))
                if err != nil {
                        fmt.Fprintf(os.Stderr, "testing: %s\n", err)
                        os.Exit(2)
                }
                runtime.GC() // materialize all statistics
                if err = m.deps.WriteProfileTo("allocs", f, 0); err != nil {
                        fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *memProfile, err)
                        os.Exit(2)
                }
                f.Close()
        }
        if *blockProfile != "" && *blockProfileRate >= 0 {
                f, err := os.Create(toOutputDir(*blockProfile))
                if err != nil {
                        fmt.Fprintf(os.Stderr, "testing: %s\n", err)
                        os.Exit(2)
                }
                if err = m.deps.WriteProfileTo("block", f, 0); err != nil {
                        fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *blockProfile, err)
                        os.Exit(2)
                }
                f.Close()
        }
        if *mutexProfile != "" && *mutexProfileFraction >= 0 {
                f, err := os.Create(toOutputDir(*mutexProfile))
                if err != nil {
                        fmt.Fprintf(os.Stderr, "testing: %s\n", err)
                        os.Exit(2)
                }
                if err = m.deps.WriteProfileTo("mutex", f, 0); err != nil {
                        fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *mutexProfile, err)
                        os.Exit(2)
                }
                f.Close()
        }
        if cover.Mode != "" {
                coverReport()
        }
}

// toOutputDir returns the file name relocated, if required, to outputDir.
// Simple implementation to avoid pulling in path/filepath.
func toOutputDir(path string) string {
        if *outputDir == "" || path == "" {
                return path
        }
        // On Windows, it's clumsy, but we can be almost always correct
        // by just looking for a drive letter and a colon.
        // Absolute paths always have a drive letter (ignoring UNC).
        // Problem: if path == "C:A" and outputdir == "C:\Go" it's unclear
        // what to do, but even then path/filepath doesn't help.
        // TODO: Worth doing better? Probably not, because we're here only
        // under the management of go test.
        if runtime.GOOS == "windows" && len(path) >= 2 {
                letter, colon := path[0], path[1]
                if ('a' <= letter && letter <= 'z' || 'A' <= letter && letter <= 'Z') && colon == ':' {
                        // If path starts with a drive letter we're stuck with it regardless.
                        return path
                }
        }
        if os.IsPathSeparator(path[0]) {
                return path
        }
        return fmt.Sprintf("%s%c%s", *outputDir, os.PathSeparator, path)
}

// startAlarm starts an alarm if requested.
func (m *M) startAlarm() time.Time {
        if *timeout <= 0 {
                return time.Time{}
        }

        deadline := time.Now().Add(*timeout)
        m.timer = time.AfterFunc(*timeout, func() {
                m.after()
                debug.SetTraceback("all")
                panic(fmt.Sprintf("test timed out after %v", *timeout))
        })
        return deadline
}

// stopAlarm turns off the alarm.
func (m *M) stopAlarm() {
        if *timeout > 0 {
                m.timer.Stop()
        }
}

func parseCpuList() {
        for _, val := range strings.Split(*cpuListStr, ",") {
                val = strings.TrimSpace(val)
                if val == "" {
                        continue
                }
                cpu, err := strconv.Atoi(val)
                if err != nil || cpu <= 0 {
                        fmt.Fprintf(os.Stderr, "testing: invalid value %q for -test.cpu\n", val)
                        os.Exit(1)
                }
                cpuList = append(cpuList, cpu)
        }
        if cpuList == nil {
                cpuList = append(cpuList, runtime.GOMAXPROCS(-1))
        }
}

func shouldFailFast() bool {
        return *failFast && atomic.LoadUint32(&numFailed) > 0
}