tree b52b43c7fa9571f4c55bc96105e205bac72e7245
parent fa262e61fd8e123c53023c122ab6330a8ae28aa3
author Bryan C. Mills <bcmills@google.com> 1597805232 -0400
committer Dmitri Shuralyov <dmitshur@golang.org> 1601938228 +0000

[release-branch.go1.15] testing: flush test summaries to stdout atomically when streaming output

While debugging #40771, I realized that the chatty printer should only
ever print to a single io.Writer (normally os.Stdout). The other
Writer implementations in the chain write to local buffers, but if we
wrote a test's output to a local buffer, then we did *not* write it to
stdout and we should not store it as the most recently logged test.

Because the chatty printer should only ever print to one place, it
shouldn't receive an io.Writer as an argument — rather, it shouldn't
be used at all for destinations other than the main output stream.

On the other hand, when we flush the output buffer to stdout in the
top-level flushToParent call, it is important that we not allow some
other test's output to intrude between the test summary header and the
remainder of the test's output. cmd/test2json doesn't know how to
parse such an intrusion, and it's confusing to humans too.

No test because I couldn't reproduce the user-reported error without
modifying the testing package. (This behavior seems to be very
sensitive to output size and/or goroutine scheduling.)

Fixes #40881
Updates #40771
Updates #38458

Change-Id: Ic19bf1d535672b096ba1c8583a3b74aab6d6d766
Reviewed-on: https://go-review.googlesource.com/c/go/+/249026
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
(cherry picked from commit 51c0bdc6d15dcd7f753c25896039ab41ac787ebb)
Reviewed-on: https://go-review.googlesource.com/c/go/+/252637
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Bryan C. Mills <bcmills@google.com>