added type hint for test_col_id

Author: Patrick Leonardy

tests/preprocessing/test_pig_tables.py

@@ -3,10 +3,12 @@
 import pandas as pd
 from cobra.evaluation.pigs_tables import generate_pig_tables
 
+from typing import Optional
+
 class TestPigTablesGeneration:
 
     @pytest.mark.parametrize("id_col_name", [None, "col_id"]) # test None as this is the default value in generate pig tabels 
-    def test_col_id(self, id_col_name):
+    def test_col_id(self, id_col_name: Optional[str]):
 
         # input
         data = pd.DataFrame({
@@ -36,4 +38,5 @@ def test_col_id(self, id_col_name):
             'avg_target': [0.0, 0.5, 1.0, 0.0, 0.6666666666666666, 0.0, 1.0, 0.0]
         })
 
-        pd.testing.assert_frame_equal(out, expected)
+        pd.testing.assert_frame_equal(out, expected)
+