Test that version_info is not pickled

That is, that its value is not pickle serialized/deserialized, but
always recomputed with a subprocess call the first time it is
accessed even on a Git instance that is created by unpickling.

Author: EliahKagan

Diff for: test/test_git.py

@@ -533,6 +533,18 @@ def test_version_info_cache_is_per_instance(self):
                     git2.version_info
                 git1.version_info
 
+    def test_version_info_cache_is_not_pickled(self):
+        with _rollback_refresh():
+            with _fake_git(123, 456, 789) as path:
+                git1 = Git()
+                refresh(path)
+                git1.version_info
+                git2 = pickle.loads(pickle.dumps(git1))
+                os.remove(path)  # Arrange that the second subprocess call will fail.
+                with self.assertRaises(GitCommandNotFound):
+                    git2.version_info
+                git1.version_info
+
     def test_successful_refresh_with_arg_invalidates_cached_version_info(self):
         with _rollback_refresh():
             with _fake_git(11, 111, 1) as path1: