Approx decimal sequence mapping (#8422)

changelog/8421.feature.rst

@@ -0,0 +1 @@
+:func:`pytest.approx` now works on :class:`~decimal.Decimal` within mappings/dicts and sequences/lists.

src/_pytest/python_api.py

@@ -72,6 +72,8 @@ class ApproxBase:
         return not (actual == self)
 
     def _approx_scalar(self, x) -> "ApproxScalar":
+        if isinstance(x, Decimal):
+            return ApproxDecimal(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

@@ -313,6 +313,12 @@ class TestApprox:
         assert approx(expected, rel=5e-7, abs=0) == actual
         assert approx(expected, rel=5e-8, abs=0) != actual
 
+    def test_list_decimal(self):
+        actual = [Decimal("1.000001"), Decimal("2.000001")]
+        expected = [Decimal("1"), Decimal("2")]
+
+        assert actual == approx(expected)
+
     def test_list_wrong_len(self):
         assert [1, 2] != approx([1])
         assert [1, 2] != approx([1, 2, 3])
@@ -346,6 +352,14 @@ class TestApprox:
         assert approx(expected, rel=5e-7, abs=0) == actual
         assert approx(expected, rel=5e-8, abs=0) != actual
 
+    def test_dict_decimal(self):
+        actual = {"a": Decimal("1.000001"), "b": Decimal("2.000001")}
+        # Dictionaries became ordered in python3.6, so switch up the order here
+        # to make sure it doesn't matter.
+        expected = {"b": Decimal("2"), "a": Decimal("1")}
+
+        assert actual == approx(expected)
+
     def test_dict_wrong_len(self):
         assert {"a": 1, "b": 2} != approx({"a": 1})
         assert {"a": 1, "b": 2} != approx({"a": 1, "c": 2})