add test when sort_use_col fail

tests/test_heatmap.py

@@ -143,6 +143,9 @@ class TestHeatmap(CRAWTest):
         received_data = htmp._sort_using_col(data, col='name')
         assert_frame_equal(expected_data, received_data)
 
+        with self.assertRaises(RuntimeError) as ctx:
+            htmp._sort_using_col(data)
+        self.assertEqual(str(ctx.exception), "You must specify the column used to sort.")
 
     def test_sort_using_file(self):
         data = pd.DataFrame([