diff --git a/tests/test_field_for_schema.py b/tests/test_field_for_schema.py
index 6a03cbb..6381051 100644
--- a/tests/test_field_for_schema.py
+++ b/tests/test_field_for_schema.py
@@ -55,31 +55,32 @@ def _assertAttrsEqual(self, a, b, msg=None):
 
         attrs_a = {attr for attr in vars(a) if not attr.startswith("_")}
         attrs_b = {attr for attr in vars(b) if not attr.startswith("_")}
-        if attrs_a - attrs_b:
-            self.fail(
-                f"Attributes in first value but not in second: {' '.join(map(repr, attrs_a - attrs_b))}"
-            )
-        if attrs_b - attrs_a:
-            self.fail(
-                f"Attributes in second value but not in first: {' '.join(map(repr, attrs_b - attrs_a))}"
-            )
+        if attrs_a != attrs_b:
+            if msg is None:
+                msg = "values do not have the same set of attributes"
+            self.fail(msg)
+
+        checked = []
+
+        def assert_equal(v1, v2):
+            if (v1, v2) not in checked:
+                checked.append((v1, v2))
+                if (
+                    type(v1) is type(v2)
+                    and isinstance(v1, Sequence)
+                    and isinstance(v1, Sequence)
+                    and len(v1) == len(v1)
+                ):
+                    # TestCase.assertSequenceEqual tests item equality with __eq__.
+                    # (It doesn't dispatch to an assert* method based on the item type.)
+                    # So we'll do the comparison ourself using assertEqual.
+                    for left, right in zip(v1, v2):
+                        assert_equal(left, right)
+                else:
+                    self.assertEqual(v1, v2, msg)
 
         for attr in attrs_a | attrs_b:
-            value_a = a.__dict__[attr]
-            value_b = b.__dict__[attr]
-            if (
-                type(value_a) is type(value_b)
-                and isinstance(value_a, Sequence)
-                and isinstance(value_b, Sequence)
-                and len(value_a) == len(value_b)
-            ):
-                # TestCase.assertSequenceEqual tests item equality with __eq__.
-                # (It doesn't dispatch to an assert* method based on the item type.)
-                # So we'll do the comparison ourself using assertEqual.
-                for v1, v2 in zip(value_a, value_b):
-                    self.assertEqual(v1, v2, msg)
-            else:
-                self.assertEqual(value_a, value_b, msg)
+            assert_equal(vars(a)[attr], vars(b)[attr])
 
     def test_int(self):
         self.assertFieldsEqual(