TST: add test with mock

Author: ivanovmg

pandas/tests/util/test_assert_frame_equal.py

@@ -1,3 +1,5 @@
+from unittest.mock import patch
+
 import pytest
 
 import pandas as pd
@@ -285,3 +287,15 @@ def test_allows_duplicate_labels():
 
     with pytest.raises(AssertionError, match="<Flags"):
         tm.assert_frame_equal(left, right)
+
+
+def test_assert_frame_equal_checks_index_exactly_twice():
+    data = {"col1": [1, 2, 3], "col2": [4, 5, 6]}
+    left = DataFrame(data, index=["a", "b", "c"])
+    right = DataFrame(data, index=["a", "b", "c"])
+    with patch("pandas._testing.assert_index_equal", return_value=None) as mock:
+        tm.assert_frame_equal(left, right)
+        # Expect exactly two calls:
+        # 1. Index equality
+        # 2. Columns equality
+        assert mock.call_count == 2