fix(testing): pytest.approx correctly take account Mapping keys order to compare them

Author: cmnemoi

src/_pytest/python_api.py

@@ -250,9 +250,8 @@ 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.get(approx_key, None)
             if approx_value != other_value:
                 if approx_value.expected is not None and other_value is not None:
                     try:

testing/python/approx.py

@@ -1048,6 +1048,17 @@ def test_strange_sequence(self):
         assert b == pytest.approx(a, abs=2)
         assert b != pytest.approx(a, abs=0.5)
 
+    def test_approx_on_unordered_mapping_with_mismatch(self) -> None:
+        """https://github.com/pytest-dev/pytest/pull/12445"""
+        expected = {"a": 1, "c": 3}
+        actual = {"c": 5, "a": 1}
+
+        with pytest.raises(
+            AssertionError,
+            match="Mismatched elements: 1 / 2:\n  Max absolute difference: 2\n",
+        ):
+            assert expected == approx(actual)
+
 
 class MyVec3:  # incomplete
     """sequence like"""