Fix approx default tolerances for Decimal

_pytest/python_api.py

@@ -153,6 +153,8 @@ class ApproxScalar(ApproxBase):
     """
     Perform approximate comparisons for single numbers only.
     """
+    DEFAULT_ABSOLUTE_TOLERANCE = 1e-12
+    DEFAULT_RELATIVE_TOLERANCE = 1e-6
 
     def __repr__(self):
         """
@@ -223,7 +225,7 @@ class ApproxScalar(ApproxBase):
 
         # Figure out what the absolute tolerance should be.  ``self.abs`` is
         # either None or a value specified by the user.
-        absolute_tolerance = set_default(self.abs, 1e-12)
+        absolute_tolerance = set_default(self.abs, self.DEFAULT_ABSOLUTE_TOLERANCE)
 
         if absolute_tolerance < 0:
             raise ValueError("absolute tolerance can't be negative: {}".format(absolute_tolerance))
@@ -241,7 +243,7 @@ class ApproxScalar(ApproxBase):
         # we've made sure the user didn't ask for an absolute tolerance only,
         # because we don't want to raise errors about the relative tolerance if
         # we aren't even going to use it.
-        relative_tolerance = set_default(self.rel, 1e-6) * abs(self.expected)
+        relative_tolerance = set_default(self.rel, self.DEFAULT_RELATIVE_TOLERANCE) * abs(self.expected)
 
         if relative_tolerance < 0:
             raise ValueError("relative tolerance can't be negative: {}".format(absolute_tolerance))
@@ -252,6 +254,13 @@ class ApproxScalar(ApproxBase):
         return max(relative_tolerance, absolute_tolerance)
 
 
+class ApproxDecimal(ApproxScalar):
+    from decimal import Decimal
+
+    DEFAULT_ABSOLUTE_TOLERANCE = Decimal('1e-12')
+    DEFAULT_RELATIVE_TOLERANCE = Decimal('1e-6')
+
+
 def approx(expected, rel=None, abs=None, nan_ok=False):
     """
     Assert that two numbers (or two sets of numbers) are equal to each other
@@ -401,6 +410,7 @@ def approx(expected, rel=None, abs=None, nan_ok=False):
 
     from collections import Mapping, Sequence
     from _pytest.compat import STRING_TYPES as String
+    from decimal import Decimal
 
     # Delegate the comparison to a class that knows how to deal with the type
     # of the expected value (e.g. int, float, list, dict, numpy.array, etc).
@@ -422,6 +432,8 @@ def approx(expected, rel=None, abs=None, nan_ok=False):
         cls = ApproxMapping
     elif isinstance(expected, Sequence) and not isinstance(expected, String):
         cls = ApproxSequence
+    elif isinstance(expected, Decimal):
+        cls = ApproxDecimal
     else:
         cls = ApproxScalar
 

changelog/3247.bugfix.rst

@@ -0,0 +1 @@
+Fix issue with approx on Decimal value.

testing/python/approx.py

@@ -249,6 +249,7 @@ class TestApprox(object):
             (Decimal('-1.000001'), Decimal('-1.0')),
         ]
         for a, x in within_1e6:
+            assert a == approx(x)
             assert a == approx(x, rel=Decimal('5e-6'), abs=0)
             assert a != approx(x, rel=Decimal('5e-7'), abs=0)
             assert approx(x, rel=Decimal('5e-6'), abs=0) == a