[7.2.x] Add check for zero denominator in approx (#10689)

Co-authored-by: Jay <[email protected]>

Author: github-actions[bot]

changelog/10533.bugfix.rst

@@ -0,0 +1 @@
+Fix :func:`pytest.approx` handling of dictionaries containing one or more values of `0.0` in class ApproxMapping.

src/_pytest/python_api.py

@@ -269,10 +269,16 @@ def _repr_compare(self, other_side: Mapping[object, float]) -> List[str]:
                 max_abs_diff = max(
                     max_abs_diff, abs(approx_value.expected - other_value)
                 )
-                max_rel_diff = max(
-                    max_rel_diff,
-                    abs((approx_value.expected - other_value) / approx_value.expected),
-                )
+                if approx_value.expected == 0.0:
+                    max_rel_diff = math.inf
+                else:
+                    max_rel_diff = max(
+                        max_rel_diff,
+                        abs(
+                            (approx_value.expected - other_value)
+                            / approx_value.expected
+                        ),
+                    )
                 different_ids.append(approx_key)
 
         message_data = [

testing/python/approx.py

@@ -630,6 +630,19 @@ def test_dict_nonnumeric(self):
     def test_dict_vs_other(self):
         assert 1 != approx({"a": 0})
 
+    def test_dict_for_div_by_zero(self, assert_approx_raises_regex):
+        assert_approx_raises_regex(
+            {"foo": 42.0},
+            {"foo": 0.0},
+            [
+                r"  comparison failed. Mismatched elements: 1 / 1:",
+                rf"  Max absolute difference: {SOME_FLOAT}",
+                r"  Max relative difference: inf",
+                r"  Index \| Obtained\s+\| Expected   ",
+                rf"  foo   | {SOME_FLOAT} \| {SOME_FLOAT} ± {SOME_FLOAT}",
+            ],
+        )
+
     def test_numpy_array(self):
         np = pytest.importorskip("numpy")