From 7f20b022dcbd83333ba5722ad47506877ea1b908 Mon Sep 17 00:00:00 2001
From: Ryan Gilmour <ryan.g@scene.community>
Date: Fri, 21 Jan 2022 13:19:08 +0000
Subject: [PATCH 1/2] Add test for concat with categorical + datetime
 dataframes

---
 .../tests/reshape/concat/test_categorical.py  | 30 +++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/pandas/tests/reshape/concat/test_categorical.py b/pandas/tests/reshape/concat/test_categorical.py
index 5bafd2e8e8503..6286fd6c3ecc8 100644
--- a/pandas/tests/reshape/concat/test_categorical.py
+++ b/pandas/tests/reshape/concat/test_categorical.py
@@ -1,4 +1,7 @@
+from datetime import datetime
+
 import numpy as np
+import pytest
 
 from pandas.core.dtypes.dtypes import CategoricalDtype
 
@@ -203,6 +206,33 @@ def test_categorical_concat_gh7864(self):
         dfa = df1._append(df2)
         tm.assert_index_equal(df["grade"].cat.categories, dfa["grade"].cat.categories)
 
+    @pytest.mark.parametrize(
+        ("input_1", "input_2", "expected"),
+        (  # both Catergorical dtypes with datetimes
+            (
+                DataFrame(
+                    {"x": Series(datetime(2021, 1, 1), index=[0], dtype="category")}
+                ),
+                DataFrame(
+                    {"x": Series(datetime(2021, 1, 2), index=[1], dtype="category")}
+                ),
+                DataFrame({"x": Series([datetime(2021, 1, 1), datetime(2021, 1, 2)])}),
+            ),
+            # both Catergorical dtypes, one datetime, one string
+            (
+                DataFrame(
+                    {"x": Series(datetime(2021, 1, 1), index=[0], dtype="category")}
+                ),
+                DataFrame({"x": Series("test string", index=[1], dtype="category")}),
+                DataFrame({"x": Series([datetime(2021, 1, 1), "test string"])}),
+            ),
+        ),
+    )
+    def test_categorical_datetime_concat(self, input_1, input_2, expected):
+        # GH 39443
+        result = pd.concat([input_1, input_2])
+        tm.assert_equal(result, expected)
+
     def test_categorical_index_upcast(self):
         # GH 17629
         # test upcasting to object when concatinating on categorical indexes

From e5807e4809eee3a635547c756df86fa65fc512f5 Mon Sep 17 00:00:00 2001
From: Ryan Gilmour <ryan.g@scene.community>
Date: Fri, 21 Jan 2022 14:33:13 +0000
Subject: [PATCH 2/2] Remove pytest parametisation

---
 .../tests/reshape/concat/test_categorical.py  | 48 +++++++++----------
 1 file changed, 23 insertions(+), 25 deletions(-)

diff --git a/pandas/tests/reshape/concat/test_categorical.py b/pandas/tests/reshape/concat/test_categorical.py
index 6286fd6c3ecc8..c2030828d1cac 100644
--- a/pandas/tests/reshape/concat/test_categorical.py
+++ b/pandas/tests/reshape/concat/test_categorical.py
@@ -1,7 +1,6 @@
 from datetime import datetime
 
 import numpy as np
-import pytest
 
 from pandas.core.dtypes.dtypes import CategoricalDtype
 
@@ -206,31 +205,30 @@ def test_categorical_concat_gh7864(self):
         dfa = df1._append(df2)
         tm.assert_index_equal(df["grade"].cat.categories, dfa["grade"].cat.categories)
 
-    @pytest.mark.parametrize(
-        ("input_1", "input_2", "expected"),
-        (  # both Catergorical dtypes with datetimes
-            (
-                DataFrame(
-                    {"x": Series(datetime(2021, 1, 1), index=[0], dtype="category")}
-                ),
-                DataFrame(
-                    {"x": Series(datetime(2021, 1, 2), index=[1], dtype="category")}
-                ),
-                DataFrame({"x": Series([datetime(2021, 1, 1), datetime(2021, 1, 2)])}),
-            ),
-            # both Catergorical dtypes, one datetime, one string
-            (
-                DataFrame(
-                    {"x": Series(datetime(2021, 1, 1), index=[0], dtype="category")}
-                ),
-                DataFrame({"x": Series("test string", index=[1], dtype="category")}),
-                DataFrame({"x": Series([datetime(2021, 1, 1), "test string"])}),
-            ),
-        ),
-    )
-    def test_categorical_datetime_concat(self, input_1, input_2, expected):
+    def test_categorical_datetime_concat(self):
         # GH 39443
-        result = pd.concat([input_1, input_2])
+        # test catergorical dataframes both containing datetimes
+        df1 = DataFrame(
+            {"x": Series(datetime(2021, 1, 1), index=[0], dtype="category")}
+        )
+        df2 = DataFrame(
+            {"x": Series(datetime(2021, 1, 2), index=[1], dtype="category")}
+        )
+        expected = DataFrame(
+            {"x": Series([datetime(2021, 1, 1), datetime(2021, 1, 2)])}
+        )
+        result = pd.concat([df1, df2])
+        tm.assert_equal(result, expected)
+
+    def test_categorical_datetime_and_string_concat(self):
+        # GH 39443
+        # test catergorical dataframes one with datetime, one with a string
+        df1 = DataFrame(
+            {"x": Series(datetime(2021, 1, 1), index=[0], dtype="category")}
+        )
+        df2 = DataFrame({"x": Series("test string", index=[1], dtype="category")})
+        expected = DataFrame({"x": Series([datetime(2021, 1, 1), "test string"])})
+        result = pd.concat([df1, df2])
         tm.assert_equal(result, expected)
 
     def test_categorical_index_upcast(self):