BUG: Join with a list of a single element behaves as a join with a si…

…ngle element (pandas-dev#57676)

pandas/core/frame.py

@@ -10560,6 +10560,9 @@ def join(
         from pandas.core.reshape.concat import concat
         from pandas.core.reshape.merge import merge
 
+        if isinstance(other, list) and len(other) == 1:
+            other = other[0]
+
         if isinstance(other, Series):
             if other.name is None:
                 raise ValueError("Other Series must have a name")

pandas/tests/frame/methods/test_join.py

@@ -562,3 +562,21 @@ def test_frame_join_tzaware(self):
 
         tm.assert_index_equal(result.index, expected)
         assert result.index.tz.zone == "US/Central"
+
+    def test_join_list_with_single_element(self):
+        test1 = DataFrame(
+            {"cat": pd.Categorical(["a", "v", "d"])},
+            index=Index(["a", "b", "c"], name="y"),
+        )
+        test2 = DataFrame(
+            {"foo": np.arange(6)},
+            index=MultiIndex.from_tuples(
+                [(0, "a"), (0, "b"), (0, "c"), (1, "a"), (1, "b"), (1, "c")],
+                names=("x", "y"),
+            ),
+        )
+
+        result = test2.join([test1])
+        expected = test2.join(test1)
+
+        assert result.equals(expected)