Adding test case for zero rows.

Author: Saumitra Shahapure

pandas/io/tests/test_gbq.py

@@ -296,6 +296,12 @@ def test_download_dataset_larger_than_200k_rows(self):
         df = gbq.read_gbq("SELECT id FROM [publicdata:samples.wikipedia] GROUP EACH BY id ORDER BY id ASC LIMIT 200005", project_id=PROJECT_ID)
         self.assertEqual(len(df.drop_duplicates()), 200005)
 
+    def test_zero_rows(self):
+        df = gbq.read_gbq("SELECT * FROM [publicdata:samples.wikipedia] where timestamp=-9999999", project_id=PROJECT_ID)
+        tm.assertIs(df, DataFrame, "Zero rows result should be dataframe.")
+        self.assertEqual(len(df), 0)
+
+
 class TestToGBQIntegration(tm.TestCase):
     # This class requires bq.py to be installed for setup/teardown. 
     # It will also need to be preconfigured with a default dataset,