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

Author: cmnemoi

src/_pytest/python_api.py

@@ -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.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

@@ -1,21 +1,18 @@
 # mypy: allow-untyped-defs
 from __future__ import annotations
 
-from contextlib import contextmanager
 import decimal
-from decimal import Decimal
-from fractions import Fraction
-from math import inf
-from math import nan
-from math import sqrt
 import operator
-from operator import eq
-from operator import ne
 import re
+from contextlib import contextmanager
+from decimal import Decimal
+from fractions import Fraction
+from math import inf, nan, sqrt
+from operator import eq, ne
 
+import pytest
 from _pytest.pytester import Pytester
 from _pytest.python_api import _recursive_sequence_map
-import pytest
 from pytest import approx
 
 
@@ -1062,6 +1059,17 @@ def test_approx_dicts_with_mismatch_on_keys(self) -> None:
         ):
             assert actual == approx(expected)
 
+    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"""