test(hrr): skip the ownership stamp test where git has no ownership check

projects/hrr/tests/scripts/test_version_stamp.py

@@ -13,14 +13,39 @@
 PLAYBACK = STAMP.parent
 
 
+ASSUME_OTHER_OWNER = {"GIT_TEST_ASSUME_DIFFERENT_OWNER": "1"}
+
+
+def git_env(extra_env):
+    env = os.environ.copy()
+    env.pop("GIT_CONFIG_GLOBAL", None)
+    env.pop("GIT_CONFIG_SYSTEM", None)
+    env.update(extra_env)
+    return env
+
+
+def git_enforces_ownership():
+    """True when git refuses a repository it believes someone else owns.
+
+    Not every git does: one older than the ownership check ignores the
+    variable, and one whose system or global config says safe.directory = *
+    (as on GitHub's hosted runners) trusts every directory. Where git trusts
+    everything, the stamp reading the repository is correct and the test has
+    nothing to prove.
+    """
+    with tempfile.TemporaryDirectory() as tmp:
+        env = git_env(ASSUME_OTHER_OWNER)
+        subprocess.run(["git", "init", "-q", tmp], check=True, env=env)
+        proc = subprocess.run(["git", "rev-parse", "--git-dir"], cwd=tmp,
+                              check=False, capture_output=True, env=env)
+        return proc.returncode != 0
+
+
 class VersionStampTest(unittest.TestCase):
     def stamp(self, extra_env):
         with tempfile.TemporaryDirectory() as tmp:
             out = Path(tmp) / "hrr_build_info.h"
-            env = os.environ.copy()
-            env.pop("GIT_CONFIG_GLOBAL", None)
-            env.pop("GIT_CONFIG_SYSTEM", None)
-            env.update(extra_env)
+            env = git_env(extra_env)
             proc = subprocess.run(
                 ["cmake", "-DSRC_DIR=" + str(PLAYBACK), "-DOUT_FILE=" + str(out),
                  "-P", str(STAMP)],
@@ -33,10 +58,12 @@ def test_owned_repo_still_stamps(self):
         self.assertIn('#define HRR_BUILD_REV "', text)
         self.assertNotIn('HRR_BUILD_REV "unknown"', text)
 
+    @unittest.skipUnless(git_enforces_ownership(),
+                         "this git does not enforce the ownership check")
     def test_checkout_owned_by_someone_else_reports_unknown(self):
         # Git treats the checkout as owned by another user. A stamp that
         # bypasses the ownership check, by whatever route, still reads it.
-        text = self.stamp({"GIT_TEST_ASSUME_DIFFERENT_OWNER": "1"})
+        text = self.stamp(ASSUME_OTHER_OWNER)
         self.assertIn('HRR_BUILD_REV "unknown"', text)