time: clarify documentation for allowed formats and add tests to prove them
The existing documentation for the time.Layout const states "Only these values
are recognized", but then doesn't include the numeric forms for month leading to
ambiguity and assumptions that may not be true. It's unclear, for example,
that space padding is only available for day of the month.
Finally I add tests to show the behaviors in specific scenarios.
Change-Id: I4e08a14834c17b6bdf3b6b47d39dafa8c1a138fb
Reviewed-on: https://go-review.googlesource.com/c/go/+/418875 Reviewed-by: Rob Pike <r@golang.org> Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
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