From: Kristofer Karlsson <krka@spotify.com>

Several tests create fixture data consisting of a single repeated
character with "test-tool genzeros <count> | tr '\000' <char>".  This
works well on platforms where tr(1) is implemented efficiently.

The implementation of tr(1) on macOS supports multi-byte characters,
and processes its input one character at a time through
getwchar() and putwchar(), even in the C locale.  For small inputs
that does not matter, but t4205 generates more than 2GB of data this
way, which makes that test much slower on macOS than on Linux: on the
macOS CI runners, tr(1) alone spends 95 to 123 seconds of CPU time on
it, compared to about 6 seconds on Linux.

Fix this by adding "test-tool genbytes <char> [<count>]" next to
"genzeros", sharing the same code, which writes the requested
character directly.  Use it in all tests that piped "genzeros"
through tr(1), not just t4205, so that it is the obvious choice for
new tests.  Callers that want NUL bytes keep using "genzeros".

While at it, parse the count with git_parse_signed(), so that an
invalid count is reported as a usage error instead of being silently
treated as 0.

This makes t4205 much faster on macOS in CI.  The Linux jobs, shown
for comparison, show smaller differences, which may partly be due to
normal run-to-run variation:

  job                before    after   change
  osx-gcc            821.1s   243.3s   -70.4%
  osx-reftable       911.0s   194.0s   -78.7%
  linux-asan-ubsan   226.7s   222.1s    -2.0%
  linux-leaks        320.2s   298.8s    -6.7%

Signed-off-by: Kristofer Karlsson <krka@spotify.com>

Submitted-As: https://lore.kernel.org/git/pull.2301.v3.git.1794335168170.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.2301.git.1794063565.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.2301.v2.git.1794165304.gitgitgadget@gmail.com