fix: approx() tolerance not applied to sequences/mappings nested inside dicts

changelog/8703.bugfix.rst

@@ -0,0 +1 @@
+Fixed ``pytest.approx()`` silently falling back to exact equality when a dict value is itself a list or dict. Nested sequences and mappings are now compared with the same tolerance as top-level ones.

src/_pytest/python_api.py

@@ -98,6 +98,10 @@ def _approx_scalar(self, x) -> ApproxBase:
             return ApproxDecimal(x, rel=self.rel, abs=self.abs, nan_ok=self.nan_ok)
         if isinstance(x, (datetime, timedelta)):
             return ApproxTimedelta(x, rel=self.rel, abs=self.abs, nan_ok=self.nan_ok)
+        if isinstance(x, Mapping):
+            return ApproxMapping(x, rel=self.rel, abs=self.abs, nan_ok=self.nan_ok)
+        if _is_sequence_like(x):
+            return ApproxSequenceLike(x, rel=self.rel, abs=self.abs, nan_ok=self.nan_ok)
         return ApproxScalar(x, rel=self.rel, abs=self.abs, nan_ok=self.nan_ok)
 
     def _yield_comparisons(self, actual):

testing/python/approx.py

@@ -679,6 +679,10 @@ def test_list_wrong_len(self):
         assert [1, 2] != approx([1])
         assert [1, 2] != approx([1, 2, 3])
 
+    def test_list_with_dict_elements(self):
+        assert [{"a": 1.0 + 1e-7}] == approx([{"a": 1.0}], abs=1e-5)
+        assert [{"a": 1.0 + 1e-4}] != approx([{"a": 1.0}], abs=1e-5)
+
     def test_tuple(self):
         actual = (1 + 1e-7, 2 + 1e-8)
         expected = (1, 2)
@@ -726,6 +730,10 @@ def test_dict_nonnumeric(self):
         assert {"a": 1.0, "b": 1} != pytest.approx({"a": 1.0, "b": None})
         assert {"a": 1.0, "b": True} != pytest.approx({"a": 1.0, "b": False}, abs=2)
 
+    def test_dict_with_list_values(self):
+        assert {"a": [1.0, 2.0 + 1e-7]} == approx({"a": [1.0, 2.0]}, abs=1e-5)
+        assert {"a": [1.0, 2.0 + 1e-4]} != approx({"a": [1.0, 2.0]}, abs=1e-5)
+
     def test_dict_vs_other(self):
         assert 1 != approx({"a": 0})