1 // Copyright 2009 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
5 // Package testing provides support for automated testing of Go packages.
6 // It is intended to be used in concert with the "go test" command, which automates
7 // execution of any function of the form
8 // func TestXxx(*testing.T)
9 // where Xxx does not start with a lowercase letter. The function name
10 // serves to identify the test routine.
12 // Within these functions, use the Error, Fail or related methods to signal failure.
14 // To write a new test suite, create a file whose name ends _test.go that
15 // contains the TestXxx functions as described here. Put the file in the same
16 // package as the one being tested. The file will be excluded from regular
17 // package builds but will be included when the "go test" command is run.
18 // For more detail, run "go help test" and "go help testflag".
20 // A simple test function looks like this:
22 // func TestAbs(t *testing.T) {
25 // t.Errorf("Abs(-1) = %d; want 1", got)
31 // Functions of the form
32 // func BenchmarkXxx(*testing.B)
33 // are considered benchmarks, and are executed by the "go test" command when
34 // its -bench flag is provided. Benchmarks are run sequentially.
36 // For a description of the testing flags, see
37 // https://golang.org/cmd/go/#hdr-Testing_flags
39 // A sample benchmark function looks like this:
40 // func BenchmarkRandInt(b *testing.B) {
41 // for i := 0; i < b.N; i++ {
46 // The benchmark function must run the target code b.N times.
47 // During benchmark execution, b.N is adjusted until the benchmark function lasts
48 // long enough to be timed reliably. The output
49 // BenchmarkRandInt-8 68453040 17.8 ns/op
50 // means that the loop ran 68453040 times at a speed of 17.8 ns per loop.
52 // If a benchmark needs some expensive setup before running, the timer
55 // func BenchmarkBigLen(b *testing.B) {
58 // for i := 0; i < b.N; i++ {
63 // If a benchmark needs to test performance in a parallel setting, it may use
64 // the RunParallel helper function; such benchmarks are intended to be used with
65 // the go test -cpu flag:
67 // func BenchmarkTemplateParallel(b *testing.B) {
68 // templ := template.Must(template.New("test").Parse("Hello, {{.}}!"))
69 // b.RunParallel(func(pb *testing.PB) {
70 // var buf bytes.Buffer
73 // templ.Execute(&buf, "World")
80 // The package also runs and verifies example code. Example functions may
81 // include a concluding line comment that begins with "Output:" and is compared with
82 // the standard output of the function when the tests are run. (The comparison
83 // ignores leading and trailing space.) These are examples of an example:
85 // func ExampleHello() {
86 // fmt.Println("hello")
90 // func ExampleSalutations() {
91 // fmt.Println("hello, and")
92 // fmt.Println("goodbye")
98 // The comment prefix "Unordered output:" is like "Output:", but matches any
101 // func ExamplePerm() {
102 // for _, value := range Perm(5) {
103 // fmt.Println(value)
105 // // Unordered output: 4
112 // Example functions without output comments are compiled but not executed.
114 // The naming convention to declare examples for the package, a function F, a type T and
115 // method M on type T are:
117 // func Example() { ... }
118 // func ExampleF() { ... }
119 // func ExampleT() { ... }
120 // func ExampleT_M() { ... }
122 // Multiple example functions for a package/type/function/method may be provided by
123 // appending a distinct suffix to the name. The suffix must start with a
124 // lower-case letter.
126 // func Example_suffix() { ... }
127 // func ExampleF_suffix() { ... }
128 // func ExampleT_suffix() { ... }
129 // func ExampleT_M_suffix() { ... }
131 // The entire test file is presented as the example when it contains a single
132 // example function, at least one other function, type, variable, or constant
133 // declaration, and no test or benchmark functions.
137 // Tests or benchmarks may be skipped at run time with a call to
138 // the Skip method of *T or *B:
140 // func TestTimeConsuming(t *testing.T) {
141 // if testing.Short() {
142 // t.Skip("skipping test in short mode.")
147 // Subtests and Sub-benchmarks
149 // The Run methods of T and B allow defining subtests and sub-benchmarks,
150 // without having to define separate functions for each. This enables uses
151 // like table-driven benchmarks and creating hierarchical tests.
152 // It also provides a way to share common setup and tear-down code:
154 // func TestFoo(t *testing.T) {
156 // t.Run("A=1", func(t *testing.T) { ... })
157 // t.Run("A=2", func(t *testing.T) { ... })
158 // t.Run("B=1", func(t *testing.T) { ... })
159 // // <tear-down code>
162 // Each subtest and sub-benchmark has a unique name: the combination of the name
163 // of the top-level test and the sequence of names passed to Run, separated by
164 // slashes, with an optional trailing sequence number for disambiguation.
166 // The argument to the -run and -bench command-line flags is an unanchored regular
167 // expression that matches the test's name. For tests with multiple slash-separated
168 // elements, such as subtests, the argument is itself slash-separated, with
169 // expressions matching each name element in turn. Because it is unanchored, an
170 // empty expression matches any string.
171 // For example, using "matching" to mean "whose name contains":
173 // go test -run '' # Run all tests.
174 // go test -run Foo # Run top-level tests matching "Foo", such as "TestFooBar".
175 // go test -run Foo/A= # For top-level tests matching "Foo", run subtests matching "A=".
176 // go test -run /A=1 # For all top-level tests, run subtests matching "A=1".
178 // Subtests can also be used to control parallelism. A parent test will only
179 // complete once all of its subtests complete. In this example, all tests are
180 // run in parallel with each other, and only with each other, regardless of
181 // other top-level tests that may be defined:
183 // func TestGroupedParallel(t *testing.T) {
184 // for _, tc := range tests {
185 // tc := tc // capture range variable
186 // t.Run(tc.Name, func(t *testing.T) {
193 // The race detector kills the program if it exceeds 8192 concurrent goroutines,
194 // so use care when running parallel tests with the -race flag set.
196 // Run does not return until parallel subtests have completed, providing a way
197 // to clean up after a group of parallel tests:
199 // func TestTeardownParallel(t *testing.T) {
200 // // This Run will not return until the parallel tests finish.
201 // t.Run("group", func(t *testing.T) {
202 // t.Run("Test1", parallelTest1)
203 // t.Run("Test2", parallelTest2)
204 // t.Run("Test3", parallelTest3)
206 // // <tear-down code>
211 // It is sometimes necessary for a test program to do extra setup or teardown
212 // before or after testing. It is also sometimes necessary for a test to control
213 // which code runs on the main thread. To support these and other cases,
214 // if a test file contains a function:
216 // func TestMain(m *testing.M)
218 // then the generated test will call TestMain(m) instead of running the tests
219 // directly. TestMain runs in the main goroutine and can do whatever setup
220 // and teardown is necessary around a call to m.Run. m.Run will return an exit
221 // code that may be passed to os.Exit. If TestMain returns, the test wrapper
222 // will pass the result of m.Run to os.Exit itself.
224 // When TestMain is called, flag.Parse has not been run. If TestMain depends on
225 // command-line flags, including those of the testing package, it should call
226 // flag.Parse explicitly. Command line flags are always parsed by the time test
227 // or benchmark functions run.
229 // A simple implementation of TestMain is:
231 // func TestMain(m *testing.M) {
232 // // call flag.Parse() here if TestMain uses flags
259 // Init registers testing flags. These flags are automatically registered by
260 // the "go test" command before running test functions, so Init is only needed
261 // when calling functions such as Benchmark without using "go test".
263 // Init has no effect if it was already called.
269 // The short flag requests that tests run more quickly, but its functionality
270 // is provided by test writers themselves. The testing package is just its
271 // home. The all.bash installation script sets it to make installation more
272 // efficient, but by default the flag is off so a plain "go test" will do a
273 // full test of the package.
274 short = flag.Bool("test.short", false, "run smaller test suite to save time")
276 // The failfast flag requests that test execution stop after the first test failure.
277 failFast = flag.Bool("test.failfast", false, "do not start new tests after the first test failure")
279 // The directory in which to create profile files and the like. When run from
280 // "go test", the binary always runs in the source directory for the package;
281 // this flag lets "go test" tell the binary to write the files in the directory where
282 // the "go test" command is run.
283 outputDir = flag.String("test.outputdir", "", "write profiles to `dir`")
284 // Report as tests are run; default is silent for success.
285 chatty = flag.Bool("test.v", false, "verbose: print additional output")
286 count = flag.Uint("test.count", 1, "run tests and benchmarks `n` times")
287 coverProfile = flag.String("test.coverprofile", "", "write a coverage profile to `file`")
288 matchList = flag.String("test.list", "", "list tests, examples, and benchmarks matching `regexp` then exit")
289 match = flag.String("test.run", "", "run only tests and examples matching `regexp`")
290 memProfile = flag.String("test.memprofile", "", "write an allocation profile to `file`")
291 memProfileRate = flag.Int("test.memprofilerate", 0, "set memory allocation profiling `rate` (see runtime.MemProfileRate)")
292 cpuProfile = flag.String("test.cpuprofile", "", "write a cpu profile to `file`")
293 blockProfile = flag.String("test.blockprofile", "", "write a goroutine blocking profile to `file`")
294 blockProfileRate = flag.Int("test.blockprofilerate", 1, "set blocking profile `rate` (see runtime.SetBlockProfileRate)")
295 mutexProfile = flag.String("test.mutexprofile", "", "write a mutex contention profile to the named file after execution")
296 mutexProfileFraction = flag.Int("test.mutexprofilefraction", 1, "if >= 0, calls runtime.SetMutexProfileFraction()")
297 panicOnExit0 = flag.Bool("test.paniconexit0", false, "panic on call to os.Exit(0)")
298 traceFile = flag.String("test.trace", "", "write an execution trace to `file`")
299 timeout = flag.Duration("test.timeout", 0, "panic test binary after duration `d` (default 0, timeout disabled)")
300 cpuListStr = flag.String("test.cpu", "", "comma-separated `list` of cpu counts to run each test with")
301 parallel = flag.Int("test.parallel", runtime.GOMAXPROCS(0), "run at most `n` tests in parallel")
302 testlog = flag.String("test.testlogfile", "", "write test action log to `file` (for use only by cmd/go)")
309 // Flags, registered during Init.
322 blockProfileRate *int
324 mutexProfileFraction *int
327 timeout *time.Duration
332 haveExamples bool // are there examples?
337 numFailed uint32 // number of test failures
340 type chattyPrinter struct {
342 lastNameMu sync.Mutex // guards lastName
343 lastName string // last printed test name in chatty mode
346 func newChattyPrinter(w io.Writer) *chattyPrinter {
347 return &chattyPrinter{w: w}
350 // Updatef prints a message about the status of the named test to w.
352 // The formatted message must include the test name itself.
353 func (p *chattyPrinter) Updatef(testName, format string, args ...interface{}) {
355 defer p.lastNameMu.Unlock()
357 // Since the message already implies an association with a specific new test,
358 // we don't need to check what the old test name was or log an extra CONT line
359 // for it. (We're updating it anyway, and the current message already includes
361 p.lastName = testName
362 fmt.Fprintf(p.w, format, args...)
365 // Printf prints a message, generated by the named test, that does not
366 // necessarily mention that tests's name itself.
367 func (p *chattyPrinter) Printf(testName, format string, args ...interface{}) {
369 defer p.lastNameMu.Unlock()
371 if p.lastName == "" {
372 p.lastName = testName
373 } else if p.lastName != testName {
374 fmt.Fprintf(p.w, "=== CONT %s\n", testName)
375 p.lastName = testName
378 fmt.Fprintf(p.w, format, args...)
381 // The maximum number of stack frames to go through when skipping helper functions for
382 // the purpose of decorating log messages.
383 const maxStackLen = 50
385 // common holds the elements common between T and B and
386 // captures common methods such as Errorf.
388 mu sync.RWMutex // guards this group of fields
389 output []byte // Output generated by test or benchmark.
390 w io.Writer // For flushToParent.
391 ran bool // Test or benchmark (or one of its subtests) was executed.
392 failed bool // Test or benchmark has failed.
393 skipped bool // Test of benchmark has been skipped.
394 done bool // Test is finished and all subtests have completed.
395 helperPCs map[uintptr]struct{} // functions to be skipped when writing file/line info
396 helperNames map[string]struct{} // helperPCs converted to function names
397 cleanups []func() // optional functions to be called at the end of the test
398 cleanupName string // Name of the cleanup function.
399 cleanupPc []uintptr // The stack trace at the point where Cleanup was called.
401 chatty *chattyPrinter // A copy of chattyPrinter, if the chatty flag is set.
402 bench bool // Whether the current test is a benchmark.
403 finished bool // Test function has completed.
404 hasSub int32 // Written atomically.
405 raceErrors int // Number of races detected during test.
406 runner string // Function name of tRunner running the test.
409 level int // Nesting depth of test or benchmark.
410 creator []uintptr // If level > 0, the stack trace at the point where the parent called t.Run.
411 name string // Name of test or benchmark.
412 start time.Time // Time test or benchmark started
413 duration time.Duration
414 barrier chan bool // To signal parallel subtests they may start.
415 signal chan bool // To signal a test is done.
416 sub []*T // Queue of subtests to be run in parallel.
424 // Short reports whether the -test.short flag is set.
427 panic("testing: Short called before Init")
429 // Catch code that calls this from TestMain without first calling flag.Parse.
431 panic("testing: Short called before Parse")
437 // CoverMode reports what the test coverage mode is set to. The
438 // values are "set", "count", or "atomic". The return value will be
439 // empty if test coverage is not enabled.
440 func CoverMode() string {
444 // Verbose reports whether the -test.v flag is set.
445 func Verbose() bool {
448 panic("testing: Verbose called before Init")
451 panic("testing: Verbose called before Parse")
456 // frameSkip searches, starting after skip frames, for the first caller frame
457 // in a function not marked as a helper and returns that frame.
458 // The search stops if it finds a tRunner function that
459 // was the entry point into the test and the test is not a subtest.
460 // This function must be called with c.mu held.
461 func (c *common) frameSkip(skip int) runtime.Frame {
462 // If the search continues into the parent test, we'll have to hold
463 // its mu temporarily. If we then return, we need to unlock it.
464 shouldUnlock := false
470 var pc [maxStackLen]uintptr
471 // Skip two extra frames to account for this function
472 // and runtime.Callers itself.
473 n := runtime.Callers(skip+2, pc[:])
475 panic("testing: zero callers found")
477 frames := runtime.CallersFrames(pc[:n])
478 var firstFrame, prevFrame, frame runtime.Frame
479 for more := true; more; prevFrame = frame {
480 frame, more = frames.Next()
481 if frame.Function == c.cleanupName {
482 frames = runtime.CallersFrames(c.cleanupPc)
485 if firstFrame.PC == 0 {
488 if frame.Function == c.runner {
489 // We've gone up all the way to the tRunner calling
490 // the test function (so the user must have
491 // called tb.Helper from inside that test function).
492 // If this is a top-level test, only skip up to the test function itself.
493 // If we're in a subtest, continue searching in the parent test,
494 // starting from the point of the call to Run which created this subtest.
496 frames = runtime.CallersFrames(c.creator)
498 // We're no longer looking at the current c after this point,
499 // so we should unlock its mu, unless it's the original receiver,
500 // in which case our caller doesn't expect us to do that.
505 // Remember to unlock c.mu when we no longer need it, either
506 // because we went up another nesting level, or because we
514 if _, ok := c.helperNames[frame.Function]; !ok {
515 // Found a frame that wasn't inside a helper function.
522 // decorate prefixes the string with the file and line of the call site
523 // and inserts the final newline if needed and indentation spaces for formatting.
524 // This function must be called with c.mu held.
525 func (c *common) decorate(s string, skip int) string {
526 // TODO(jayconrod,katiehockman): Consider refactoring the logging logic.
527 // If more helper PCs have been added since we last did the conversion
528 if c.helperNames == nil {
529 c.helperNames = make(map[string]struct{})
530 for pc := range c.helperPCs {
531 c.helperNames[pcToName(pc)] = struct{}{}
535 frame := c.frameSkip(skip)
539 // Truncate file name at last file name separator.
540 if index := strings.LastIndex(file, "/"); index >= 0 {
541 file = file[index+1:]
542 } else if index = strings.LastIndex(file, "\\"); index >= 0 {
543 file = file[index+1:]
551 buf := new(strings.Builder)
552 // Every line is indented at least 4 spaces.
554 fmt.Fprintf(buf, "%s:%d: ", file, line)
555 lines := strings.Split(s, "\n")
556 if l := len(lines); l > 1 && lines[l-1] == "" {
559 for i, line := range lines {
561 // Second and subsequent lines are indented an additional 4 spaces.
562 buf.WriteString("\n ")
564 buf.WriteString(line)
570 // flushToParent writes c.output to the parent after first writing the header
571 // with the given format and arguments.
572 func (c *common) flushToParent(testName, format string, args ...interface{}) {
580 if len(c.output) > 0 {
582 args = append(args[:len(args):len(args)], c.output)
583 c.output = c.output[:0] // but why?
586 if c.chatty != nil && p.w == c.chatty.w {
587 // We're flushing to the actual output, so track that this output is
588 // associated with a specific test (and, specifically, that the next output
589 // is *not* associated with that test).
591 // Moreover, if c.output is non-empty it is important that this write be
592 // atomic with respect to the output of other tests, so that we don't end up
593 // with confusing '=== CONT' lines in the middle of our '--- PASS' block.
594 // Neither humans nor cmd/test2json can parse those easily.
595 // (See https://golang.org/issue/40771.)
596 c.chatty.Updatef(testName, format, args...)
598 // We're flushing to the output buffer of the parent test, which will
599 // itself follow a test-name header when it is finally flushed to stdout.
600 fmt.Fprintf(p.w, format, args...)
604 type indenter struct {
608 func (w indenter) Write(b []byte) (n int, err error) {
611 end := bytes.IndexByte(b, '\n')
617 // An indent of 4 spaces will neatly align the dashes with the status
618 // indicator of the parent.
620 w.c.output = append(w.c.output, indent...)
621 w.c.output = append(w.c.output, b[:end]...)
627 // fmtDuration returns a string representing d in the form "87.00s".
628 func fmtDuration(d time.Duration) string {
629 return fmt.Sprintf("%.2fs", d.Seconds())
632 // TB is the interface common to T and B.
635 Error(args ...interface{})
636 Errorf(format string, args ...interface{})
640 Fatal(args ...interface{})
641 Fatalf(format string, args ...interface{})
643 Log(args ...interface{})
644 Logf(format string, args ...interface{})
646 Skip(args ...interface{})
648 Skipf(format string, args ...interface{})
652 // A private method to prevent users implementing the
653 // interface and so future additions to it will not
654 // violate Go 1 compatibility.
661 // T is a type passed to Test functions to manage test state and support formatted test logs.
663 // A test ends when its Test function returns or calls any of the methods
664 // FailNow, Fatal, Fatalf, SkipNow, Skip, or Skipf. Those methods, as well as
665 // the Parallel method, must be called only from the goroutine running the
668 // The other reporting methods, such as the variations of Log and Error,
669 // may be called simultaneously from multiple goroutines.
673 context *testContext // For running tests and subtests.
676 func (c *common) private() {}
678 // Name returns the name of the running test or benchmark.
679 func (c *common) Name() string {
683 func (c *common) setRan() {
692 // Fail marks the function as having failed but continues execution.
693 func (c *common) Fail() {
699 // c.done needs to be locked to synchronize checks to c.done in parent tests.
701 panic("Fail in goroutine after " + c.name + " has completed")
706 // Failed reports whether the function has failed.
707 func (c *common) Failed() bool {
711 return failed || c.raceErrors+race.Errors() > 0
714 // FailNow marks the function as having failed and stops its execution
715 // by calling runtime.Goexit (which then runs all deferred calls in the
716 // current goroutine).
717 // Execution will continue at the next test or benchmark.
718 // FailNow must be called from the goroutine running the
719 // test or benchmark function, not from other goroutines
720 // created during the test. Calling FailNow does not stop
721 // those other goroutines.
722 func (c *common) FailNow() {
725 // Calling runtime.Goexit will exit the goroutine, which
726 // will run the deferred functions in this goroutine,
727 // which will eventually run the deferred lines in tRunner,
728 // which will signal to the test loop that this test is done.
730 // A previous version of this code said:
733 // c.signal <- c.self
736 // This previous version duplicated code (those lines are in
737 // tRunner no matter what), but worse the goroutine teardown
738 // implicit in runtime.Goexit was not guaranteed to complete
739 // before the test exited. If a test deferred an important cleanup
740 // function (like removing temporary files), there was no guarantee
741 // it would run on a test failure. Because we send on c.signal during
742 // a top-of-stack deferred function now, we know that the send
743 // only happens after any other stacked defers have completed.
748 // log generates the output. It's always at the same stack depth.
749 func (c *common) log(s string) {
750 c.logDepth(s, 3) // logDepth + log + public function
753 // logDepth generates the output at an arbitrary stack depth.
754 func (c *common) logDepth(s string, depth int) {
758 // This test has already finished. Try and log this message
759 // with our parent. If we don't have a parent, panic.
760 for parent := c.parent; parent != nil; parent = parent.parent {
762 defer parent.mu.Unlock()
764 parent.output = append(parent.output, parent.decorate(s, depth+1)...)
768 panic("Log in goroutine after " + c.name + " has completed")
772 // Benchmarks don't print === CONT, so we should skip the test
773 // printer and just print straight to stdout.
774 fmt.Print(c.decorate(s, depth+1))
776 c.chatty.Printf(c.name, "%s", c.decorate(s, depth+1))
781 c.output = append(c.output, c.decorate(s, depth+1)...)
785 // Log formats its arguments using default formatting, analogous to Println,
786 // and records the text in the error log. For tests, the text will be printed only if
787 // the test fails or the -test.v flag is set. For benchmarks, the text is always
788 // printed to avoid having performance depend on the value of the -test.v flag.
789 func (c *common) Log(args ...interface{}) { c.log(fmt.Sprintln(args...)) }
791 // Logf formats its arguments according to the format, analogous to Printf, and
792 // records the text in the error log. A final newline is added if not provided. For
793 // tests, the text will be printed only if the test fails or the -test.v flag is
794 // set. For benchmarks, the text is always printed to avoid having performance
795 // depend on the value of the -test.v flag.
796 func (c *common) Logf(format string, args ...interface{}) { c.log(fmt.Sprintf(format, args...)) }
798 // Error is equivalent to Log followed by Fail.
799 func (c *common) Error(args ...interface{}) {
800 c.log(fmt.Sprintln(args...))
804 // Errorf is equivalent to Logf followed by Fail.
805 func (c *common) Errorf(format string, args ...interface{}) {
806 c.log(fmt.Sprintf(format, args...))
810 // Fatal is equivalent to Log followed by FailNow.
811 func (c *common) Fatal(args ...interface{}) {
812 c.log(fmt.Sprintln(args...))
816 // Fatalf is equivalent to Logf followed by FailNow.
817 func (c *common) Fatalf(format string, args ...interface{}) {
818 c.log(fmt.Sprintf(format, args...))
822 // Skip is equivalent to Log followed by SkipNow.
823 func (c *common) Skip(args ...interface{}) {
824 c.log(fmt.Sprintln(args...))
828 // Skipf is equivalent to Logf followed by SkipNow.
829 func (c *common) Skipf(format string, args ...interface{}) {
830 c.log(fmt.Sprintf(format, args...))
834 // SkipNow marks the test as having been skipped and stops its execution
835 // by calling runtime.Goexit.
836 // If a test fails (see Error, Errorf, Fail) and is then skipped,
837 // it is still considered to have failed.
838 // Execution will continue at the next test or benchmark. See also FailNow.
839 // SkipNow must be called from the goroutine running the test, not from
840 // other goroutines created during the test. Calling SkipNow does not stop
841 // those other goroutines.
842 func (c *common) SkipNow() {
848 func (c *common) skip() {
854 // Skipped reports whether the test was skipped.
855 func (c *common) Skipped() bool {
861 // Helper marks the calling function as a test helper function.
862 // When printing file and line information, that function will be skipped.
863 // Helper may be called simultaneously from multiple goroutines.
864 func (c *common) Helper() {
867 if c.helperPCs == nil {
868 c.helperPCs = make(map[uintptr]struct{})
870 // repeating code from callerName here to save walking a stack frame
872 n := runtime.Callers(2, pc[:]) // skip runtime.Callers + Helper
874 panic("testing: zero callers found")
876 if _, found := c.helperPCs[pc[0]]; !found {
877 c.helperPCs[pc[0]] = struct{}{}
878 c.helperNames = nil // map will be recreated next time it is needed
882 // Cleanup registers a function to be called when the test and all its
883 // subtests complete. Cleanup functions will be called in last added,
884 // first called order.
885 func (c *common) Cleanup(f func()) {
886 var pc [maxStackLen]uintptr
887 // Skip two extra frames to account for this function and runtime.Callers itself.
888 n := runtime.Callers(2, pc[:])
899 name := callerName(0)
902 c.cleanupPc = cleanupPc
910 c.cleanups = append(c.cleanups, fn)
913 var tempDirReplacer struct {
918 // TempDir returns a temporary directory for the test to use.
919 // The directory is automatically removed by Cleanup when the test and
920 // all its subtests complete.
921 // Each subsequent call to t.TempDir returns a unique directory;
922 // if the directory creation fails, TempDir terminates the test by calling Fatal.
923 func (c *common) TempDir() string {
924 // Use a single parent directory for all the temporary directories
925 // created by a test, each numbered sequentially.
928 if c.tempDir == "" { // Usually the case with js/wasm
931 _, err := os.Stat(c.tempDir)
932 nonExistent = os.IsNotExist(err)
933 if err != nil && !nonExistent {
934 c.Fatalf("TempDir: %v", err)
941 // os.MkdirTemp doesn't like path separators in its pattern,
942 // so mangle the name to accommodate subtests.
943 tempDirReplacer.Do(func() {
944 tempDirReplacer.r = strings.NewReplacer("/", "_", "\\", "_", ":", "_")
946 pattern := tempDirReplacer.r.Replace(c.Name())
948 c.tempDir, c.tempDirErr = os.MkdirTemp("", pattern)
949 if c.tempDirErr == nil {
951 if err := os.RemoveAll(c.tempDir); err != nil {
952 c.Errorf("TempDir RemoveAll cleanup: %v", err)
959 if c.tempDirErr != nil {
960 c.Fatalf("TempDir: %v", c.tempDirErr)
962 seq := atomic.AddInt32(&c.tempDirSeq, 1)
963 dir := fmt.Sprintf("%s%c%03d", c.tempDir, os.PathSeparator, seq)
964 if err := os.Mkdir(dir, 0777); err != nil {
965 c.Fatalf("TempDir: %v", err)
970 // panicHanding is an argument to runCleanup.
971 type panicHandling int
974 normalPanic panicHandling = iota
975 recoverAndReturnPanic
978 // runCleanup is called at the end of the test.
979 // If catchPanic is true, this will catch panics, and return the recovered
981 func (c *common) runCleanup(ph panicHandling) (panicVal interface{}) {
982 if ph == recoverAndReturnPanic {
988 // Make sure that if a cleanup function panics,
989 // we still run the remaining cleanup functions.
992 recur := len(c.cleanups) > 0
995 c.runCleanup(normalPanic)
1002 if len(c.cleanups) > 0 {
1003 last := len(c.cleanups) - 1
1004 cleanup = c.cleanups[last]
1005 c.cleanups = c.cleanups[:last]
1015 // callerName gives the function name (qualified with a package path)
1016 // for the caller after skip frames (where 0 means the current function).
1017 func callerName(skip int) string {
1019 n := runtime.Callers(skip+2, pc[:]) // skip + runtime.Callers + callerName
1021 panic("testing: zero callers found")
1023 return pcToName(pc[0])
1026 func pcToName(pc uintptr) string {
1027 pcs := []uintptr{pc}
1028 frames := runtime.CallersFrames(pcs)
1029 frame, _ := frames.Next()
1030 return frame.Function
1033 // Parallel signals that this test is to be run in parallel with (and only with)
1034 // other parallel tests. When a test is run multiple times due to use of
1035 // -test.count or -test.cpu, multiple instances of a single test never run in
1036 // parallel with each other.
1037 func (t *T) Parallel() {
1039 panic("testing: t.Parallel called multiple times")
1042 if t.parent.barrier == nil {
1043 // T.Parallel has no effect when fuzzing.
1044 // Multiple processes may run in parallel, but only one input can run at a
1045 // time per process so we can attribute crashes to specific inputs.
1049 // We don't want to include the time we spend waiting for serial tests
1050 // in the test duration. Record the elapsed time thus far and reset the
1051 // timer afterwards.
1052 t.duration += time.Since(t.start)
1054 // Add to the list of tests to be released by the parent.
1055 t.parent.sub = append(t.parent.sub, t)
1056 t.raceErrors += race.Errors()
1058 if t.chatty != nil {
1059 // Unfortunately, even though PAUSE indicates that the named test is *no
1060 // longer* running, cmd/test2json interprets it as changing the active test
1061 // for the purpose of log parsing. We could fix cmd/test2json, but that
1062 // won't fix existing deployments of third-party tools that already shell
1063 // out to older builds of cmd/test2json — so merely fixing cmd/test2json
1064 // isn't enough for now.
1065 t.chatty.Updatef(t.name, "=== PAUSE %s\n", t.name)
1068 t.signal <- true // Release calling test.
1069 <-t.parent.barrier // Wait for the parent test to complete.
1070 t.context.waitParallel()
1072 if t.chatty != nil {
1073 t.chatty.Updatef(t.name, "=== CONT %s\n", t.name)
1076 t.start = time.Now()
1077 t.raceErrors += -race.Errors()
1080 // InternalTest is an internal type but exported because it is cross-package;
1081 // it is part of the implementation of the "go test" command.
1082 type InternalTest struct {
1087 var errNilPanicOrGoexit = errors.New("test executed panic(nil) or runtime.Goexit")
1089 func tRunner(t *T, fn func(t *T)) {
1090 t.runner = callerName(0)
1092 // When this goroutine is done, either because fn(t)
1093 // returned normally or because a test failure triggered
1094 // a call to runtime.Goexit, record the duration and send
1095 // a signal saying that the test is done.
1098 atomic.AddUint32(&numFailed, 1)
1101 if t.raceErrors+race.Errors() > 0 {
1102 t.Errorf("race detected during execution of test")
1105 // If the test panicked, print any test output before dying.
1109 if !t.finished && err == nil {
1110 err = errNilPanicOrGoexit
1111 for p := t.parent; p != nil; p = p.parent {
1113 t.Errorf("%v: subtest may have called FailNow on a parent test", err)
1120 // Use a deferred call to ensure that we report that the test is
1121 // complete even if a cleanup function calls t.FailNow. See issue 41355.
1130 // Only report that the test is complete if it doesn't panic,
1131 // as otherwise the test binary can exit before the panic is
1132 // reported to the user. See issue 41479.
1136 doPanic := func(err interface{}) {
1138 if r := t.runCleanup(recoverAndReturnPanic); r != nil {
1139 t.Logf("cleanup panicked with %v", r)
1141 // Flush the output log up to the root before dying.
1142 for root := &t.common; root.parent != nil; root = root.parent {
1144 root.duration += time.Since(root.start)
1147 root.flushToParent(root.name, "--- FAIL: %s (%s)\n", root.name, fmtDuration(d))
1148 if r := root.parent.runCleanup(recoverAndReturnPanic); r != nil {
1149 fmt.Fprintf(root.parent.w, "cleanup panicked with %v", r)
1159 t.duration += time.Since(t.start)
1162 // Run parallel subtests.
1163 // Decrease the running count for this test.
1165 // Release the parallel subtests.
1167 // Wait for subtests to complete.
1168 for _, sub := range t.sub {
1171 cleanupStart := time.Now()
1172 err := t.runCleanup(recoverAndReturnPanic)
1173 t.duration += time.Since(cleanupStart)
1178 // Reacquire the count for sequential tests. See comment in Run.
1179 t.context.waitParallel()
1181 } else if t.isParallel {
1182 // Only release the count for this test if it was run as a parallel
1183 // test. See comment in Run method.
1186 t.report() // Report after all subtests have finished.
1188 // Do not lock t.done to allow race detector to detect race in case
1189 // the user does not appropriately synchronizes a goroutine.
1191 if t.parent != nil && atomic.LoadInt32(&t.hasSub) == 0 {
1196 if len(t.sub) == 0 {
1197 t.runCleanup(normalPanic)
1201 t.start = time.Now()
1202 t.raceErrors = -race.Errors()
1205 // code beyond here will not be executed when FailNow is invoked
1209 // Run runs f as a subtest of t called name. It runs f in a separate goroutine
1210 // and blocks until f returns or calls t.Parallel to become a parallel test.
1211 // Run reports whether f succeeded (or at least did not fail before calling t.Parallel).
1213 // Run may be called simultaneously from multiple goroutines, but all such calls
1214 // must return before the outer test function for t returns.
1215 func (t *T) Run(name string, f func(t *T)) bool {
1216 atomic.StoreInt32(&t.hasSub, 1)
1217 testName, ok, _ := t.context.match.fullName(&t.common, name)
1218 if !ok || shouldFailFast() {
1221 // Record the stack trace at the point of this call so that if the subtest
1222 // function - which runs in a separate stack - is marked as a helper, we can
1223 // continue walking the stack into the parent test.
1224 var pc [maxStackLen]uintptr
1225 n := runtime.Callers(2, pc[:])
1228 barrier: make(chan bool),
1229 signal: make(chan bool),
1238 t.w = indenter{&t.common}
1240 if t.chatty != nil {
1241 t.chatty.Updatef(t.name, "=== RUN %s\n", t.name)
1243 // Instead of reducing the running count of this test before calling the
1244 // tRunner and increasing it afterwards, we rely on tRunner keeping the
1245 // count correct. This ensures that a sequence of sequential tests runs
1246 // without being preempted, even when their parent is a parallel test. This
1247 // may especially reduce surprises if *parallel == 1.
1250 // At this point, it is likely that FailNow was called on one of the
1251 // parent tests by one of the subtests. Continue aborting up the chain.
1257 // Deadline reports the time at which the test binary will have
1258 // exceeded the timeout specified by the -timeout flag.
1260 // The ok result is false if the -timeout flag indicates “no timeout” (0).
1261 func (t *T) Deadline() (deadline time.Time, ok bool) {
1262 deadline = t.context.deadline
1263 return deadline, !deadline.IsZero()
1266 // testContext holds all fields that are common to all tests. This includes
1267 // synchronization primitives to run at most *parallel tests.
1268 type testContext struct {
1274 // Channel used to signal tests that are ready to be run in parallel.
1275 startParallel chan bool
1277 // running is the number of tests currently running in parallel.
1278 // This does not include tests that are waiting for subtests to complete.
1281 // numWaiting is the number tests waiting to be run in parallel.
1284 // maxParallel is a copy of the parallel flag.
1288 func newTestContext(maxParallel int, m *matcher) *testContext {
1289 return &testContext{
1291 startParallel: make(chan bool),
1292 maxParallel: maxParallel,
1293 running: 1, // Set the count to 1 for the main (sequential) test.
1297 func (c *testContext) waitParallel() {
1299 if c.running < c.maxParallel {
1309 func (c *testContext) release() {
1311 if c.numWaiting == 0 {
1318 c.startParallel <- true // Pick a waiting test to be run.
1321 // No one should be using func Main anymore.
1322 // See the doc comment on func Main and use MainStart instead.
1323 var errMain = errors.New("testing: unexpected use of func Main")
1325 type matchStringOnly func(pat, str string) (bool, error)
1327 func (f matchStringOnly) MatchString(pat, str string) (bool, error) { return f(pat, str) }
1328 func (f matchStringOnly) StartCPUProfile(w io.Writer) error { return errMain }
1329 func (f matchStringOnly) StopCPUProfile() {}
1330 func (f matchStringOnly) WriteProfileTo(string, io.Writer, int) error { return errMain }
1331 func (f matchStringOnly) ImportPath() string { return "" }
1332 func (f matchStringOnly) StartTestLog(io.Writer) {}
1333 func (f matchStringOnly) StopTestLog() error { return errMain }
1334 func (f matchStringOnly) SetPanicOnExit0(bool) {}
1335 func (f matchStringOnly) CoordinateFuzzing(time.Duration, int64, int, []corpusEntry, []reflect.Type, string, string) error {
1338 func (f matchStringOnly) RunFuzzWorker(func(corpusEntry) error) error { return errMain }
1339 func (f matchStringOnly) ReadCorpus(string, []reflect.Type) ([]corpusEntry, error) {
1343 // Main is an internal function, part of the implementation of the "go test" command.
1344 // It was exported because it is cross-package and predates "internal" packages.
1345 // It is no longer used by "go test" but preserved, as much as possible, for other
1346 // systems that simulate "go test" using Main, but Main sometimes cannot be updated as
1347 // new functionality is added to the testing package.
1348 // Systems simulating "go test" should be updated to use MainStart.
1349 func Main(matchString func(pat, str string) (bool, error), tests []InternalTest, benchmarks []InternalBenchmark, examples []InternalExample) {
1350 os.Exit(MainStart(matchStringOnly(matchString), tests, benchmarks, nil, examples).Run())
1353 // M is a type passed to a TestMain function to run the actual tests.
1356 tests []InternalTest
1357 benchmarks []InternalBenchmark
1358 fuzzTargets []InternalFuzzTarget
1359 examples []InternalExample
1366 // value to pass to os.Exit, the outer test func main
1367 // harness calls os.Exit with this code. See #34129.
1371 // testDeps is an internal interface of functionality that is
1372 // passed into this package by a test's generated main package.
1373 // The canonical implementation of this interface is
1374 // testing/internal/testdeps's TestDeps.
1375 type testDeps interface {
1377 MatchString(pat, str string) (bool, error)
1378 SetPanicOnExit0(bool)
1379 StartCPUProfile(io.Writer) error
1381 StartTestLog(io.Writer)
1383 WriteProfileTo(string, io.Writer, int) error
1384 CoordinateFuzzing(time.Duration, int64, int, []corpusEntry, []reflect.Type, string, string) error
1385 RunFuzzWorker(func(corpusEntry) error) error
1386 ReadCorpus(string, []reflect.Type) ([]corpusEntry, error)
1389 // MainStart is meant for use by tests generated by 'go test'.
1390 // It is not meant to be called directly and is not subject to the Go 1 compatibility document.
1391 // It may change signature from release to release.
1392 func MainStart(deps testDeps, tests []InternalTest, benchmarks []InternalBenchmark, fuzzTargets []InternalFuzzTarget, examples []InternalExample) *M {
1397 benchmarks: benchmarks,
1398 fuzzTargets: fuzzTargets,
1403 // Run runs the tests. It returns an exit code to pass to os.Exit.
1404 func (m *M) Run() (code int) {
1409 // Count the number of calls to m.Run.
1410 // We only ever expected 1, but we didn't enforce that,
1411 // and now there are tests in the wild that call m.Run multiple times.
1412 // Sigh. golang.org/issue/23129.
1415 // TestMain may have already called flag.Parse.
1421 fmt.Fprintln(os.Stderr, "testing: -parallel can only be given a positive integer")
1426 if *matchFuzz != "" && *fuzzCacheDir == "" {
1427 fmt.Fprintln(os.Stderr, "testing: internal error: -test.fuzzcachedir must be set if -test.fuzz is set")
1433 if len(*matchList) != 0 {
1434 listTests(m.deps.MatchString, m.tests, m.benchmarks, m.fuzzTargets, m.examples)
1444 // The fuzzing coordinator will already run all tests, examples,
1445 // and benchmarks. Don't make the workers do redundant work.
1446 deadline := m.startAlarm()
1447 haveExamples = len(m.examples) > 0
1448 testRan, testOk := runTests(m.deps.MatchString, m.tests, deadline)
1449 fuzzTargetsRan, fuzzTargetsOk := runFuzzTargets(m.deps, m.fuzzTargets)
1450 exampleRan, exampleOk := runExamples(m.deps.MatchString, m.examples)
1452 if !testRan && !exampleRan && !fuzzTargetsRan && *matchBenchmarks == "" && *matchFuzz == "" {
1453 fmt.Fprintln(os.Stderr, "testing: warning: no tests to run")
1455 if !testOk || !exampleOk || !fuzzTargetsOk || !runBenchmarks(m.deps.ImportPath(), m.deps.MatchString, m.benchmarks) || race.Errors() > 0 {
1462 fuzzingRan, fuzzingOk := runFuzzing(m.deps, m.fuzzTargets)
1463 if *matchFuzz != "" && !fuzzingRan {
1464 fmt.Fprintln(os.Stderr, "testing: warning: no targets to fuzz")
1466 if !*isFuzzWorker && !fuzzingOk {
1469 m.exitCode = fuzzWorkerExitCode
1483 func (t *T) report() {
1484 if t.parent == nil {
1487 dstr := fmtDuration(t.duration)
1488 format := "--- %s: %s (%s)\n"
1490 t.flushToParent(t.name, format, "FAIL", t.name, dstr)
1491 } else if t.chatty != nil {
1493 t.flushToParent(t.name, format, "SKIP", t.name, dstr)
1495 t.flushToParent(t.name, format, "PASS", t.name, dstr)
1500 func listTests(matchString func(pat, str string) (bool, error), tests []InternalTest, benchmarks []InternalBenchmark, fuzzTargets []InternalFuzzTarget, examples []InternalExample) {
1501 if _, err := matchString(*matchList, "non-empty"); err != nil {
1502 fmt.Fprintf(os.Stderr, "testing: invalid regexp in -test.list (%q): %s\n", *matchList, err)
1506 for _, test := range tests {
1507 if ok, _ := matchString(*matchList, test.Name); ok {
1508 fmt.Println(test.Name)
1511 for _, bench := range benchmarks {
1512 if ok, _ := matchString(*matchList, bench.Name); ok {
1513 fmt.Println(bench.Name)
1516 for _, fuzzTarget := range fuzzTargets {
1517 if ok, _ := matchString(*matchList, fuzzTarget.Name); ok {
1518 fmt.Println(fuzzTarget.Name)
1521 for _, example := range examples {
1522 if ok, _ := matchString(*matchList, example.Name); ok {
1523 fmt.Println(example.Name)
1528 // RunTests is an internal function but exported because it is cross-package;
1529 // it is part of the implementation of the "go test" command.
1530 func RunTests(matchString func(pat, str string) (bool, error), tests []InternalTest) (ok bool) {
1531 var deadline time.Time
1533 deadline = time.Now().Add(*timeout)
1535 ran, ok := runTests(matchString, tests, deadline)
1536 if !ran && !haveExamples {
1537 fmt.Fprintln(os.Stderr, "testing: warning: no tests to run")
1542 func runTests(matchString func(pat, str string) (bool, error), tests []InternalTest, deadline time.Time) (ran, ok bool) {
1544 for _, procs := range cpuList {
1545 runtime.GOMAXPROCS(procs)
1546 for i := uint(0); i < *count; i++ {
1547 if shouldFailFast() {
1550 ctx := newTestContext(*parallel, newMatcher(matchString, *match, "-test.run"))
1551 ctx.deadline = deadline
1554 signal: make(chan bool),
1555 barrier: make(chan bool),
1561 t.chatty = newChattyPrinter(t.w)
1563 tRunner(t, func(t *T) {
1564 for _, test := range tests {
1565 t.Run(test.Name, test.F)
1567 // Run catching the signal rather than the tRunner as a separate
1568 // goroutine to avoid adding a goroutine during the sequential
1569 // phase as this pollutes the stacktrace output when aborting.
1570 go func() { <-t.signal }()
1572 ok = ok && !t.Failed()
1579 // before runs before all testing.
1580 func (m *M) before() {
1581 if *memProfileRate > 0 {
1582 runtime.MemProfileRate = *memProfileRate
1584 if *cpuProfile != "" {
1585 f, err := os.Create(toOutputDir(*cpuProfile))
1587 fmt.Fprintf(os.Stderr, "testing: %s\n", err)
1590 if err := m.deps.StartCPUProfile(f); err != nil {
1591 fmt.Fprintf(os.Stderr, "testing: can't start cpu profile: %s\n", err)
1595 // Could save f so after can call f.Close; not worth the effort.
1597 if *traceFile != "" {
1598 f, err := os.Create(toOutputDir(*traceFile))
1600 fmt.Fprintf(os.Stderr, "testing: %s\n", err)
1603 if err := trace.Start(f); err != nil {
1604 fmt.Fprintf(os.Stderr, "testing: can't start tracing: %s\n", err)
1608 // Could save f so after can call f.Close; not worth the effort.
1610 if *blockProfile != "" && *blockProfileRate >= 0 {
1611 runtime.SetBlockProfileRate(*blockProfileRate)
1613 if *mutexProfile != "" && *mutexProfileFraction >= 0 {
1614 runtime.SetMutexProfileFraction(*mutexProfileFraction)
1616 if *coverProfile != "" && cover.Mode == "" {
1617 fmt.Fprintf(os.Stderr, "testing: cannot use -test.coverprofile because test binary was not built with coverage enabled\n")
1621 // Note: Not using toOutputDir.
1622 // This file is for use by cmd/go, not users.
1626 f, err = os.Create(*testlog)
1628 f, err = os.OpenFile(*testlog, os.O_WRONLY, 0)
1630 f.Seek(0, io.SeekEnd)
1634 fmt.Fprintf(os.Stderr, "testing: %s\n", err)
1637 m.deps.StartTestLog(f)
1641 m.deps.SetPanicOnExit0(true)
1645 // after runs after all testing.
1646 func (m *M) after() {
1647 m.afterOnce.Do(func() {
1651 // Restore PanicOnExit0 after every run, because we set it to true before
1652 // every run. Otherwise, if m.Run is called multiple times the behavior of
1653 // os.Exit(0) will not be restored after the second run.
1655 m.deps.SetPanicOnExit0(false)
1659 func (m *M) writeProfiles() {
1661 if err := m.deps.StopTestLog(); err != nil {
1662 fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *testlog, err)
1665 if err := testlogFile.Close(); err != nil {
1666 fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *testlog, err)
1670 if *cpuProfile != "" {
1671 m.deps.StopCPUProfile() // flushes profile to disk
1673 if *traceFile != "" {
1674 trace.Stop() // flushes trace to disk
1676 if *memProfile != "" {
1677 f, err := os.Create(toOutputDir(*memProfile))
1679 fmt.Fprintf(os.Stderr, "testing: %s\n", err)
1682 runtime.GC() // materialize all statistics
1683 if err = m.deps.WriteProfileTo("allocs", f, 0); err != nil {
1684 fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *memProfile, err)
1689 if *blockProfile != "" && *blockProfileRate >= 0 {
1690 f, err := os.Create(toOutputDir(*blockProfile))
1692 fmt.Fprintf(os.Stderr, "testing: %s\n", err)
1695 if err = m.deps.WriteProfileTo("block", f, 0); err != nil {
1696 fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *blockProfile, err)
1701 if *mutexProfile != "" && *mutexProfileFraction >= 0 {
1702 f, err := os.Create(toOutputDir(*mutexProfile))
1704 fmt.Fprintf(os.Stderr, "testing: %s\n", err)
1707 if err = m.deps.WriteProfileTo("mutex", f, 0); err != nil {
1708 fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *mutexProfile, err)
1713 if cover.Mode != "" {
1718 // toOutputDir returns the file name relocated, if required, to outputDir.
1719 // Simple implementation to avoid pulling in path/filepath.
1720 func toOutputDir(path string) string {
1721 if *outputDir == "" || path == "" {
1724 // On Windows, it's clumsy, but we can be almost always correct
1725 // by just looking for a drive letter and a colon.
1726 // Absolute paths always have a drive letter (ignoring UNC).
1727 // Problem: if path == "C:A" and outputdir == "C:\Go" it's unclear
1728 // what to do, but even then path/filepath doesn't help.
1729 // TODO: Worth doing better? Probably not, because we're here only
1730 // under the management of go test.
1731 if runtime.GOOS == "windows" && len(path) >= 2 {
1732 letter, colon := path[0], path[1]
1733 if ('a' <= letter && letter <= 'z' || 'A' <= letter && letter <= 'Z') && colon == ':' {
1734 // If path starts with a drive letter we're stuck with it regardless.
1738 if os.IsPathSeparator(path[0]) {
1741 return fmt.Sprintf("%s%c%s", *outputDir, os.PathSeparator, path)
1744 // startAlarm starts an alarm if requested.
1745 func (m *M) startAlarm() time.Time {
1750 deadline := time.Now().Add(*timeout)
1751 m.timer = time.AfterFunc(*timeout, func() {
1753 debug.SetTraceback("all")
1754 panic(fmt.Sprintf("test timed out after %v", *timeout))
1759 // stopAlarm turns off the alarm.
1760 func (m *M) stopAlarm() {
1766 func parseCpuList() {
1767 for _, val := range strings.Split(*cpuListStr, ",") {
1768 val = strings.TrimSpace(val)
1772 cpu, err := strconv.Atoi(val)
1773 if err != nil || cpu <= 0 {
1774 fmt.Fprintf(os.Stderr, "testing: invalid value %q for -test.cpu\n", val)
1777 cpuList = append(cpuList, cpu)
1780 cpuList = append(cpuList, runtime.GOMAXPROCS(-1))
1784 func shouldFailFast() bool {
1785 return *failFast && atomic.LoadUint32(&numFailed) > 0