Update test_pivot.py

TST: add additional test cases for pivot_table with categorical data pandas-dev#21370

Author: uds5501

pandas/tests/reshape/test_pivot.py

@@ -142,6 +142,23 @@ def test_pivot_table_dropna_categoricals(self, dropna):
 
         tm.assert_frame_equal(result, expected)
 
+    def test_pivot_with_non_observable_dropna_civ(self, dropna):
+      # gh-21370
+       df=pd.DataFrame(
+         {"In":pd.Categorical([np.nan,'low','high','low','high','high',np.nan],
+                              categories=['low','high'],ordered=True),
+          "Col":["A","B","C","C","C","A","B"],
+          "Val":range(7)})
+        result=df.pivot_table(index="In",columns="Col",values="Val",dropna=dropna)
+        expected=pd.DataFrame(
+          {'A':[np.nan,5],'B':[1,np.nan],'C':[3.0,3.0]},
+          index=pd.Index(
+            pd.Categorical.from_codes([0,1],
+                                      categories=['low','high'],
+                                      ordered=True),
+            name='In'))
+       tm.assert_frame_equal(result,expected) 
+    
     def test_pivot_with_non_observable_dropna(self, dropna):
         # gh-21133
         df = pd.DataFrame(