[tox] Allowing running of specific tests (#9097)

tests/dataframe_test.py

@@ -14,9 +14,11 @@
 # KIND, either express or implied.  See the License for the
 # specific language governing permissions and limitations
 # under the License.
+# isort:skip_file
 import numpy as np
 import pandas as pd
 
+import tests.test_app
 from superset.dataframe import df_to_records
 from superset.db_engine_specs import BaseEngineSpec
 from superset.result_set import SupersetResultSet