Add DataFrame creation and filtering test

tests/preprocessing_test.py

@@ -1,4 +1,7 @@
-from app.constants import files
+from pandas import DataFrame
+from requests import get
+from app.constants import URL, COLUMNS, FILES, DATASETS
+from app.request_datasets import request_dataset
 from app.preprocessing import create_dataframe
 from os import remove
 
@@ -21,3 +24,4 @@ def test_dataframe_creation():
         df = create_dataframe(dataset)
         remove(FILES[dataset])
         assert isinstance(df, DataFrame)
+        assert list(df) == COLUMNS[dataset]