fix(tests): skip install.sh safety tests when POSIX bash is unavailable

[danielmeppiel]

TL;DR

The Build & Test (windows-latest) CI job was failing with 30 test failures in tests/unit/install/test_install_safety.py, all with a uniform assert 1 == <expected>. These tests shell out to bash to exercise the Unix installer's safety validator; on windows-latest runners the ambient bash is the WSL stub and exits 1 for every call. This PR skips the bash-dependent tests where no usable POSIX bash exists.

Problem (WHY)

tests/unit/install/test_install_safety.py sources the apm_lib_dir_validate() block out of install.sh and runs it under bash to assert exit codes (0, 11, 12, 14). On windows-latest GitHub runners, the bash on PATH resolves to the WSL stub (C:\Windows\System32\bash.exe). With no Linux distribution installed, that stub exits 1 for every invocation — so all 30 bash-dependent tests failed with the same assert 1 == 0/11/12/14, while the 3 pure-Python sentinel tests passed.

install.sh is the Unix installer; Windows installs via install.ps1. There is no value in running these shell-validator tests on a Windows runner that has no POSIX bash.

Linux (x64/arm64) and macOS jobs were green — the failure was Windows-only.

Approach (WHAT)

Detect whether a real POSIX bash is invocable, and skip the bash-dependent test classes when it is not — instead of letting them fail with a misleading uniform exit code. The pure-Python sentinel-invariant tests keep running on every platform.

Implementation (HOW)

In tests/unit/install/test_install_safety.py:

• Added _usable_bash(): probes bash -c "printf ok" and returns true only when it exits 0 and prints ok. Any OSError / SubprocessError / non-zero exit (the WSL-stub case) yields False.
• Added a module-level requires_bash = pytest.mark.skipif(...) and applied it to the six bash-dependent classes (TestAbsolutePathGuard, TestSuffixGuard, TestBlocklistGuard, TestMarkerFileGuard, TestUserLocalInstall, TestReportedIncident). TestSentinelInvariants is pure-Python and stays unmarked.
• Set MSYS_NO_PATHCONV=1 / MSYS2_ARG_CONV_EXCL=* on the subprocess env so a real Git Bash (MSYS2) runner does not rewrite POSIX path arguments like /usr/local/lib/apm into Windows paths.

Trade-offs

• On a Windows runner with no POSIX bash, these validator tests are skipped rather than executed. That is correct: the code under test (install.sh) never runs on Windows, and the existing CRLF-normalization plus sentinel tests still guard the script's testability invariants. Linux and macOS continue to execute the full validator matrix.

Validation evidence

• macOS (bash usable): 43 passed — unchanged from baseline.
• Simulated WSL stub (a fake bash on PATH that exits 1): 3 passed, 40 skipped — the bash-dependent tests skip cleanly and the pure-Python sentinel tests still run.
• ruff check and ruff format --check on the changed file: clean.

How to test

# Normal (POSIX bash present): all tests run
uv run --extra dev pytest tests/unit/install/test_install_safety.py -q

# Simulate the windows-latest WSL stub locally:
mkdir -p /tmp/fakebash && printf '#!/bin/sh\nexit 1\n' > /tmp/fakebash/bash
chmod +x /tmp/fakebash/bash
PATH="/tmp/fakebash:$PATH" uv run --extra dev pytest tests/unit/install/test_install_safety.py -q
# expect: 3 passed, 40 skipped
rm -rf /tmp/fakebash

Failing run for reference: https://github.com/microsoft/apm/actions/runs/27216959181/job/80361090943

[Copilot]

Pull request overview

This PR improves cross-platform reliability of the Unix-installer safety validator unit tests by skipping bash-dependent test classes when a usable POSIX bash is not available (notably on windows-latest, where bash may resolve to the WSL stub and fail uniformly).

Changes:

• Add a _usable_bash() probe and module-level requires_bash skip marker for bash-dependent test classes.
• Ensure MSYS2/Git Bash does not rewrite POSIX-looking path arguments by setting MSYS_NO_PATHCONV / MSYS2_ARG_CONV_EXCL in the subprocess environment.

Show a summary per file

File	Description
tests/unit/install/test_install_safety.py	Adds a bash usability probe + skip marker for bash-driven tests and hardens subprocess env against MSYS path conversion.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 1