TST: test_column_types_consistent (pandas-dev#42725)

Author: shiv-io

pandas/tests/indexing/test_loc.py

@@ -143,6 +143,37 @@ def test_setitem_from_duplicate_axis(self):
         )
         tm.assert_frame_equal(df, expected)
 
+    def test_column_types_consistent(self):
+        # GH 26779
+        df = DataFrame(
+            data={
+                "channel": [1, 2, 3],
+                "A": ["String 1", np.NaN, "String 2"],
+                "B": [
+                    Timestamp("2019-06-11 11:00:00"),
+                    pd.NaT,
+                    Timestamp("2019-06-11 12:00:00"),
+                ],
+            }
+        )
+        df2 = DataFrame(
+            data={"A": ["String 3"], "B": [Timestamp("2019-06-11 12:00:00")]}
+        )
+        # Change Columns A and B to df2.values wherever Column A is NaN
+        df.loc[df["A"].isna(), ["A", "B"]] = df2.values
+        expected = DataFrame(
+            data={
+                "channel": [1, 2, 3],
+                "A": ["String 1", "String 3", "String 2"],
+                "B": [
+                    Timestamp("2019-06-11 11:00:00"),
+                    Timestamp("2019-06-11 12:00:00"),
+                    Timestamp("2019-06-11 12:00:00"),
+                ],
+            }
+        )
+        tm.assert_frame_equal(df, expected)
+
 
 class TestLoc2:
     # TODO: better name, just separating out things that rely on base class