Extra-step in empty database fixture to ensure proper teardown.

voeventdb/server/tests/fixtures/connection.py

@@ -53,6 +53,13 @@ def empty_db_connection(request):
     yield connection
     # TearDown
     transaction.rollback()
+    # The next line is effectively voodoo; it shouldn't be necessary but seems
+    # to fix some intermittent race-condition issue which occasionally causes
+    # py.test runs to fail due to database-integrity errors.
+    # (My guess is that the transaction-rollback is somehow entering a
+    # race-condition with the next test, adding this extra command ensures that
+    # the database is properly emptied before continuing.)
+    Base.metadata.drop_all(bind=connection)
     connection.close()
     engine.dispose()