feat(spanner): fix asyncio event loop leak in unit tests and activate type check

Author: chalmerlowe

packages/google-cloud-spanner/noxfile.py

@@ -753,8 +753,6 @@ def prerelease_deps(session, protobuf_implementation, database_dialect):
 @nox.session(python=ALL_PYTHON)
 def mypy(session):
     """Run the type checker."""
-    session.skip("Mypy is not yet supported")
-
     # TODO(https://github.com/googleapis/gapic-generator-python/issues/2579):
     # use the latest version of mypy
     session.install(

packages/google-cloud-spanner/tests/unit/gapic/conftest.py

@@ -11,10 +11,13 @@ def provide_loop_to_sync_grpc_tests():
     If no global loop exists, `grpc.aio` engine crashes during initialization.
     """
     try:
-        loop = asyncio.get_event_loop()
+        asyncio.get_running_loop()
+        yield
     except RuntimeError:
         loop = asyncio.new_event_loop()
         asyncio.set_event_loop(loop)
-
-    yield
-    # No close here, just ensure existance
+        try:
+            yield
+        finally:
+            loop.close()
+            asyncio.set_event_loop(None)