gh-121039: add Floats/ComplexesAreIdenticalMixin to test.support.testcase (GH-121071)

1 files changed, 40 insertions, 0 deletions

diff --git a/Lib/test/support/testcase.py b/Lib/test/support/testcase.py
index 1e4363b..fad1e4c 100644
--- a/Lib/test/support/testcase.py
+++ b/Lib/test/support/testcase.py
@@ -1,3 +1,6 @@
+from math import copysign, isnan
+
+
 class ExceptionIsLikeMixin:
     def assertExceptionIsLike(self, exc, template):
         """
@@ -23,3 +26,40 @@ class ExceptionIsLikeMixin:
             self.assertEqual(len(exc.exceptions), len(template.exceptions))
             for e, t in zip(exc.exceptions, template.exceptions):
                 self.assertExceptionIsLike(e, t)
+
+
+class FloatsAreIdenticalMixin:
+    def assertFloatsAreIdentical(self, x, y):
+        """Fail unless floats x and y are identical, in the sense that:
+        (1) both x and y are nans, or
+        (2) both x and y are infinities, with the same sign, or
+        (3) both x and y are zeros, with the same sign, or
+        (4) x and y are both finite and nonzero, and x == y
+
+        """
+        msg = 'floats {!r} and {!r} are not identical'
+
+        if isnan(x) or isnan(y):
+            if isnan(x) and isnan(y):
+                return
+        elif x == y:
+            if x != 0.0:
+                return
+            # both zero; check that signs match
+            elif copysign(1.0, x) == copysign(1.0, y):
+                return
+            else:
+                msg += ': zeros have different signs'
+        self.fail(msg.format(x, y))
+
+
+class ComplexesAreIdenticalMixin(FloatsAreIdenticalMixin):
+    def assertComplexesAreIdentical(self, x, y):
+        """Fail unless complex numbers x and y have equal values and signs.
+
+        In particular, if x and y both have real (or imaginary) part
+        zero, but the zeros have different signs, this test will fail.
+
+        """
+        self.assertFloatsAreIdentical(x.real, y.real)
+        self.assertFloatsAreIdentical(x.imag, y.imag)