The known-dirs-probe test built its expected path from os.environ['ProgramFiles']
+ os.path.join, but the production code uses os.path.expandvars('%ProgramFiles%..').
On the Linux CI runners expandvars does not expand %VAR% syntax and os.path.join
uses '/', so the expected path diverged from what the code produced and the test
failed (assert None == 'C:\Program Files/Git/cmd/git.exe').
Mock the OS-specific surfaces (winreg, os.path.exists/expandvars/join) so the
Windows code path is exercised deterministically on any host. Verified the two
previously-failing assertions now pass under posix os.path semantics, and a
mutation check (reverting the fix) still makes the three behavior tests fail.
Parallels tests/test_issue5175_macos_launchd_git.py for the Windows case:
verifies _resolve_git_executable() resolves git via the Git-for-Windows
registry InstallPath and known install dirs when it is off PATH, that
_detect_webui_version() recovers a real stamp instead of 'unknown', and
falsifiable guards that the registry path is Windows-only and returns None
when git is genuinely absent.
allenliang2022