gh-103791: Make contextlib.suppress also act on exceptions within an ExceptionGroup (#103792)

Co-authored-by: Irit Katriel <1055913+iritkatriel@users.noreply.github.com>

Lib/test/support/testcase.py

@@ -0,0 +1,25 @@
+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)