diff --git a/Lib/test/support/testcase.py b/Lib/test/support/testcase.py
new file mode 100644
index 0000000000..fad1e4cb34
--- /dev/null
+++ b/Lib/test/support/testcase.py
@@ -0,0 +1,65 @@
+from math import copysign, isnan
+
+
+class ExceptionIsLikeMixin:
+    def assertExceptionIsLike(self, exc, template):
+        """
+        Passes when the provided `exc` matches the structure of `template`.
+        Individual exceptions don't have to be the same objects or even pass
+        an equality test: they only need to be the same type and contain equal
+        `exc_obj.args`.
+        """
+        if exc is None and template is None:
+            return
+
+        if template is None:
+            self.fail(f"unexpected exception: {exc}")
+
+        if exc is None:
+            self.fail(f"expected an exception like {template!r}, got None")
+
+        if not isinstance(exc, ExceptionGroup):
+            self.assertEqual(exc.__class__, template.__class__)
+            self.assertEqual(exc.args[0], template.args[0])
+        else:
+            self.assertEqual(exc.message, template.message)
+            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)