Test "installing" another git and refreshing

This is trickier to test than the other cases, but important enough
that I think it deserves its own test.

Author: EliahKagan

test/test_git.py

@@ -24,6 +24,7 @@
     import mock  # To be able to examine call_args.kwargs on a mock.
 
 import ddt
+import pytest
 
 from git import Git, refresh, GitCommandError, GitCommandNotFound, Repo, cmd
 from git.util import cwd, finalize_process
@@ -611,6 +612,30 @@ def test_successful_refresh_with_same_env_invalidates_cached_version_info(self):
                 refresh()  # The fake git at path1 has a different version now.
                 self.assertEqual(new_git.version_info, (22, 222, 2))
 
+    @pytest.mark.xfail(
+        os.name == "nt",
+        reason="""Name "git" won't find .bat/.cmd (need shim, custom name, or shell)""",
+        raises=GitCommandNotFound,
+    )
+    def test_successful_refresh_in_default_scenario_invalidates_cached_version(self):
+        """Refreshing updates version after a filesystem change adds a git command."""
+        with contextlib.ExitStack() as stack:
+            stack.enter_context(_rollback_refresh())
+            path1 = Path(stack.enter_context(_fake_git(11, 111, 1)))
+            path2 = Path(stack.enter_context(_fake_git(22, 222, 2)))
+            sep = os.pathsep
+            new_path_var = f"{path1.parent}{sep}{path2.parent}{sep}{os.environ['PATH']}"
+            stack.enter_context(mock.patch.dict(os.environ, {"PATH": new_path_var}))
+            stack.enter_context(_patch_out_env("GIT_PYTHON_GIT_EXECUTABLE"))
+            new_git = Git()
+            path2.rename(path2.with_stem("git"))
+            refresh()
+            self.assertEqual(new_git.version_info, (22, 222, 2), 'before "downgrade"')
+            path1.rename(path1.with_stem("git"))
+            self.assertEqual(new_git.version_info, (22, 222, 2), "stale version")
+            refresh()
+            self.assertEqual(new_git.version_info, (11, 111, 1), "fresh version")
+
     def test_options_are_passed_to_git(self):
         # This works because any command after git --version is ignored.
         git_version = self.git(version=True).NoOp()