fix concat index name test to have partially-overlapping indices

Author: iamlemec

pandas/tests/reshape/test_concat.py

@@ -1280,29 +1280,36 @@ def test_concat_ignore_index(self, sort):
         tm.assert_frame_equal(v1, expected)
 
     @pytest.mark.parametrize(
-        "input_names,output_name",
+        "name_in1,name_in2,name_in3,name_out",
         [
-            (["idx", "idx"], "idx"),
-            (["idx", None], "idx"),
-            ([None, None], None),
-            (["idx1", "idx2"], None),
-            (["idx", "idx", None], "idx"),
-            (["idx1", "idx2", None], None),
+            ("idx", "idx", "idx", "idx"),
+            ("idx", "idx", None, "idx"),
+            ("idx", None, None, "idx"),
+            ("idx1", "idx2", None, None),
+            ("idx1", "idx1", "idx2", None),
+            ("idx1", "idx2", "idx3", None),
+            (None, None, None, None),
         ],
     )
-    def test_concat_same_index_names(self, input_names, output_name):
+    def test_concat_same_index_names(self, name_in1, name_in2, name_in3, name_out):
         # GH13475
-        indices = [pd.Index(["a", "b", "c"], name=n) for n in input_names]
+        indices = [
+            pd.Index(["a", "b", "c"], name=name_in1),
+            pd.Index(["b", "c", "d"], name=name_in2),
+            pd.Index(["c", "d", "e"], name=name_in3),
+        ]
         frames = [
             pd.DataFrame({c: [0, 1, 2]}, index=i)
             for i, c in zip(indices, ["x", "y", "z"])
         ]
         result = pd.concat(frames, axis=1)
 
-        exp_ind = pd.Index(["a", "b", "c"], name=output_name)
-        expected = pd.DataFrame(
-            {c: [0, 1, 2] for _, c in zip(input_names, ["x", "y", "z"])}, index=exp_ind
-        )
+        exp_ind = pd.Index(["a", "b", "c", "d", "e"], name=name_out)
+        expected = pd.DataFrame({
+            "x": [0, 1, 2, np.nan, np.nan],
+            "y": [np.nan, 0, 1, 2, np.nan],
+            "z": [np.nan, np.nan, 0, 1, 2],
+        }, index=exp_ind)
 
         tm.assert_frame_equal(result, expected)