[PR #13815/e95a843a backport][9.0.x] fix(testing): pytest.approx correctly take account Mapping keys order to compare them

changelog/12444.bugfix.rst

@@ -0,0 +1 @@
+Fixed :func:`pytest.approx` which now correctly takes account Mapping keys order to compare them.

src/_pytest/python_api.py

@@ -242,7 +242,7 @@ def _repr_compare(self, other_side: Mapping[object, float]) -> list[str]:
                 f"Lengths: {len(self.expected)} and {len(other_side)}",
             ]
 
-        if set(self.expected.keys()) != set(other_side.keys()):
+        if self.expected.keys() != other_side.keys():
             return [
                 "comparison failed.",
                 f"Mappings has different keys: expected {self.expected.keys()} but got {other_side.keys()}",
@@ -256,9 +256,8 @@ def _repr_compare(self, other_side: Mapping[object, float]) -> list[str]:
         max_abs_diff = -math.inf
         max_rel_diff = -math.inf
         different_ids = []
-        for (approx_key, approx_value), other_value in zip(
-            approx_side_as_map.items(), other_side.values(), strict=True
-        ):
+        for approx_key, approx_value in approx_side_as_map.items():
+            other_value = other_side[approx_key]
             if approx_value != other_value:
                 if approx_value.expected is not None and other_value is not None:
                     try:

testing/python/approx.py

@@ -1062,6 +1062,46 @@ def test_approx_dicts_with_mismatch_on_keys(self) -> None:
         ):
             assert actual == approx(expected)
 
+    def test_approx_on_unordered_mapping_with_mismatch(
+        self, pytester: Pytester
+    ) -> None:
+        """https://github.com/pytest-dev/pytest/issues/12444"""
+        pytester.makepyfile(
+            """
+            import pytest
+
+            def test_approx_on_unordered_mapping_with_mismatch():
+                expected = {"a": 1, "b": 2, "c": 3, "d": 4}
+                actual = {"d": 4, "c": 5, "a": 8, "b": 2}
+                assert actual == pytest.approx(expected)
+            """
+        )
+        result = pytester.runpytest()
+        result.assert_outcomes(failed=1)
+        result.stdout.fnmatch_lines(
+            [
+                "*comparison failed.**Mismatched elements: 2 / 4:*",
+                "*Max absolute difference: 7*",
+                "*Index | Obtained | Expected *",
+                "* a * | 8 * | 1 *",
+                "* c * | 5 * | 3 *",
+            ]
+        )
+
+    def test_approx_on_unordered_mapping_matching(self, pytester: Pytester) -> None:
+        """https://github.com/pytest-dev/pytest/issues/12444"""
+        pytester.makepyfile(
+            """
+            import pytest
+            def test_approx_on_unordered_mapping_matching():
+                expected = {"a": 1, "b": 2, "c": 3, "d": 4}
+                actual = {"d": 4, "c": 3, "a": 1, "b": 2}
+                assert actual == pytest.approx(expected)
+            """
+        )
+        result = pytester.runpytest()
+        result.assert_outcomes(passed=1)
+
 
 class MyVec3:  # incomplete
     """sequence like"""