test: add base class for the Spanner specific tests (#158)

Co-authored-by: larkee <31196561+larkee@users.noreply.github.com>

Author: Ilya Gurov

test/test_suite.py

@@ -1510,16 +1510,20 @@ class Address(Base):
         assert str(query.statement.compile(session.bind)) == EXPECTED_QUERY
 
 
-class InterleavedTablesTest(fixtures.TestBase):
-    """
-    Check that CREATE TABLE statements for interleaved tables are correctly
-    generated.
-    """
+class SpannerSpecificTestBase(fixtures.TestBase):
+    """Base class for the Cloud Spanner related tests."""
 
     def setUp(self):
         self._engine = create_engine(get_db_url())
         self._metadata = MetaData(bind=self._engine)
 
+
+class InterleavedTablesTest(SpannerSpecificTestBase):
+    """
+    Check that CREATE TABLE statements for interleaved tables are correctly
+    generated.
+    """
+
     def test_interleave(self):
         EXP_QUERY = (
             "\nCREATE TABLE client (\n\tteam_id INT64 NOT NULL, "
@@ -1562,13 +1566,9 @@ def test_interleave_on_delete_cascade(self):
             execute.assert_called_once_with(EXP_QUERY, [])
 
 
-class UserAgentTest(fixtures.TestBase):
+class UserAgentTest(SpannerSpecificTestBase):
     """Check that SQLAlchemy dialect uses correct user agent."""
 
-    def setUp(self):
-        self._engine = create_engine(get_db_url())
-        self._metadata = MetaData(bind=self._engine)
-
     def test_user_agent(self):
         dist = pkg_resources.get_distribution("sqlalchemy-spanner")