GeezerVison

Validation Steps:

1. Update Lib/test/support/strace_helper.py to set _strace_binary to /usr/bin/false (or don't have strace installed)
2. Run ./python -Werror -I -bb -m test.test_subprocess -vv POSIXProcessTestCase.test_vfork_used_when_expected

Description

The strace_helper code has a _make_error function to simplify making StraceResult objects in error cases. That takes a details parameter which is either a caught OSError or bytes. If it's bytes, _make_error would implicitly coerce that to a str inside of a f-string, resulting in a BytesWarning when the python test is invoked with -b.

It is useful to distinguish between an OSError or bytes when debugging the test, so eliminate the BytesWarning and show both by changing to format with repr().

After fixing the implicing bytes-> str conversion, if /usr/bin/strace is uninstalled/doesn't exist, get a new error running the test:

  File "<source_dir>/cpython/Lib/test/support/strace_helper.py", line 183, in _can_strace
    assert res.events(), "Should have parsed multiple calls"
           ~~~~~~~~~~^^
AssertionError: Should have parsed multiple calls

Resolved by checking the exit code of the subprocess before asserting there should be events. Reason for asserting there are events, rather than returning False from _can_strace, is to try and ensure that if strace runs successfully and produces an output that can't be parsed that is a test error rather than silently disabling all strace tests (See: gh-121381 where a feature working was tested with strace but the strace tests stopped running, leading to this infrastructure in #123413).

skip news: This is a fix to an error message on a python test suite internal helper.

• Issue: Unhandled BytesWarning when test.support.strace_helper.strace_python fails #127747