add new test

Author: charlesdong1991

pandas/tests/reshape/merge/test_merge.py

@@ -1451,11 +1451,18 @@ def test_merge_series(on, left_on, right_on, left_index, right_index, nm):
     ("a", 0, (None, "_y"), ["a", 0])
 ])
 def test_merge_suffix(col1, col2, suffixes, expected_cols):
+    # 24819
     a = pd.DataFrame({col1: [1, 2, 3]})
     b = pd.DataFrame({col2: [4, 5, 6]})
 
     df = a.merge(b, left_index=True, right_index=True, suffixes=suffixes)
     assert df.columns.tolist() == expected_cols
 
-    with pytest.raises(ValueError):
+
+def test_merge_suffix_errors():
+    # 24819
+    a = pd.DataFrame({0: [1, 2, 3]})
+    b = pd.DataFrame({0: [4, 5, 6]})
+
+    with pytest.raises(ValueError, match="columns overlap but no suffix specified"):
         a.merge(b, left_index=True, right_index=True, suffixes=(None, None))