testing: quote -test.v=test2json output when logging it

The -test.v=test2json flag causes the testing package to inject extra
control characters in the output to allow the JSON parser to more
gracefully handle extraneous writes to os.Stdout and/or os.Stderr in
the package under test (see CL 443596). However, it doesn't filter out
those control characters because almost no real-world tests will
output them.

It turns out that testing.TestFlag is one of the rare tests that does
output those control characters, because it tests the
-test.v=test2json flag itself.

Fixes #59181.

Change-Id: I35ca6748afcd3d4333563028817caac946f5e86a
Reviewed-on: https://go-review.googlesource.com/c/go/+/479035
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>

0 files changed, 0 insertions, 0 deletions