test(reset): select a working Bash instead of an unusable WSL launcher (#671)

* test(reset): probe Bash variable expansion on Windows

Use a bounded variable-expansion probe so a launcher that starts successfully but consumes $x is rejected. Rebase over #676 and keep its upstream-checkout guard alongside Bash discovery.

Thanks to MadsLorentzen for diagnosing the launcher expansion failure and verifying the stronger probe.

* changelog: place the #671 entry under [Unreleased]

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Mads Lorentzen <madslorentzen_17@hotmail.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

tests/_bash.py

@@ -0,0 +1,31 @@
+"""Find a usable Bash for tests that replay the documented reset commands."""
+import os
+from pathlib import Path
+import shutil
+import subprocess
+
+WINDOWS = os.name == "nt"
+
+
+def find_bash():
+    candidates = [shutil.which("bash")]
+    if WINDOWS:
+        # A Windows PATH may find the WSL launcher even without a usable WSL
+        # installation. Git for Windows also ships Bash beside its cmd/ entry
+        # points, but does not normally add that bin/ directory to PATH.
+        git = shutil.which("git")
+        if git:
+            candidates.append(str(Path(git).resolve().parent.parent / "bin" / "bash.exe"))
+    for candidate in dict.fromkeys(candidates):
+        if not candidate:
+            continue
+        try:
+            result = subprocess.run(
+                [candidate, "-c", 'x=ok; test "$x" = ok'],
+                stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, timeout=5,
+            )
+        except (OSError, subprocess.SubprocessError):
+            continue
+        if result.returncode == 0:
+            return candidate
+    return None

tests/test_bash.py

@@ -0,0 +1,70 @@
+"""A Bash launcher on PATH is not necessarily a usable shell (Windows WSL)."""
+from pathlib import Path
+import subprocess
+import unittest
+from unittest import mock
+
+try:
+    from tests import _bash
+except ImportError:
+    import _bash
+
+
+class BashDiscoveryTests(unittest.TestCase):
+    def test_working_path_shell_is_used(self):
+        with mock.patch.object(_bash, "WINDOWS", False), \
+             mock.patch.object(_bash.shutil, "which", return_value="/bin/bash"), \
+             mock.patch.object(_bash.subprocess, "run", return_value=mock.Mock(returncode=0)) as run:
+            self.assertEqual(_bash.find_bash(), "/bin/bash")
+        self.assertEqual(run.call_args.args[0], ["/bin/bash", "-c", 'x=ok; test "$x" = ok'])
+
+    def test_launcher_that_expands_variables_falls_back_to_git_bash(self):
+        git = Path(__file__).resolve().parent / "Git" / "cmd" / "git.exe"
+        fallback = str(git.parent.parent / "bin" / "bash.exe")
+
+        def probe(args, **kwargs):
+            script = args[2]
+            if args[0] == "wsl-bash":
+                # The launcher can exit successfully, but expands $x before
+                # Bash assigns it, so the reset command cannot work.
+                script = script.replace("$x", "")
+            return subprocess.CompletedProcess(args, 0 if script in (
+                "exit 0", 'x=ok; test "$x" = ok',
+            ) else 1)
+
+        with mock.patch.object(_bash, "WINDOWS", True), \
+             mock.patch.object(_bash.shutil, "which", side_effect=["wsl-bash", str(git)]), \
+             mock.patch.object(_bash.subprocess, "run", side_effect=probe):
+            self.assertEqual(_bash.find_bash(), fallback)
+
+    def test_missing_shell_needs_no_probe(self):
+        with mock.patch.object(_bash, "WINDOWS", False), \
+             mock.patch.object(_bash.shutil, "which", return_value=None), \
+             mock.patch.object(_bash.subprocess, "run") as run:
+            self.assertIsNone(_bash.find_bash())
+        run.assert_not_called()
+
+    def test_unusable_path_shell_falls_back_to_git_bash_on_windows(self):
+        git = Path(__file__).resolve().parent / "Git" / "cmd" / "git.exe"
+        fallback = str(git.parent.parent / "bin" / "bash.exe")
+        with mock.patch.object(_bash, "WINDOWS", True), \
+             mock.patch.object(_bash.shutil, "which", side_effect=["wsl-bash", str(git)]), \
+             mock.patch.object(_bash.subprocess, "run", side_effect=[
+                 mock.Mock(returncode=1), mock.Mock(returncode=0),
+             ]) as run:
+            self.assertEqual(_bash.find_bash(), fallback)
+        self.assertEqual([call.args[0][0] for call in run.call_args_list], ["wsl-bash", fallback])
+
+    def test_failed_or_hanging_shell_is_unavailable(self):
+        for error in (OSError("cannot start"), subprocess.TimeoutExpired("bash", 5)):
+            with self.subTest(error=type(error).__name__), \
+                 mock.patch.object(_bash, "WINDOWS", False), \
+                 mock.patch.object(_bash.shutil, "which", return_value="bash"), \
+                 mock.patch.object(_bash.subprocess, "run", side_effect=error):
+                self.assertIsNone(_bash.find_bash())
+
+    def test_nonzero_exit_without_a_fallback_is_unavailable(self):
+        with mock.patch.object(_bash, "WINDOWS", False), \
+             mock.patch.object(_bash.shutil, "which", return_value="bash"), \
+             mock.patch.object(_bash.subprocess, "run", return_value=mock.Mock(returncode=1)):
+            self.assertIsNone(_bash.find_bash())

tests/test_reset_command.py

@@ -28,21 +28,22 @@ tree, the profile files from /setup Step 3's own headings - so a new drop
 folder or a new /setup target fails this test until /reset covers it.
 """
 import re
-import shutil
 import subprocess
 import unittest
 from pathlib import Path
 from tempfile import TemporaryDirectory
 
 try:
+    from tests._bash import find_bash
     from tests._upstream import is_upstream_checkout
 except ImportError:  # `python -m unittest discover -s tests` imports test modules top-level
+    from _bash import find_bash
     from _upstream import is_upstream_checkout
 
 REPO = Path(__file__).resolve().parent.parent
 RESET = REPO / ".claude" / "commands" / "reset.md"
 SETUP = REPO / ".claude" / "commands" / "setup.md"
-BASH = shutil.which("bash")
+BASH = find_bash()
 
 
 def tracked_document_subfolders():

tests/test_reset_documents.py

@@ -8,9 +8,14 @@ import unittest
 from pathlib import Path
 from tempfile import TemporaryDirectory
 
+try:
+    from tests._bash import find_bash
+except ImportError:  # unittest discover -s tests imports modules top-level
+    from _bash import find_bash
+
 COMMAND = Path(__file__).resolve().parent.parent / ".claude/commands/reset.md"
 FOLDERS = ("cv", "linkedin", "diplomas", "references", "projects", "postings", "applications")
-BASH = shutil.which("bash")
+BASH = find_bash()
 
 
 def symlinks_available():