Simplify test case and add similar case for unique_together

tests/test_model_serializer.py

@@ -542,6 +542,15 @@ class UniqueTogetherModel(models.Model):
         unique_together = ("foreign_key", "one_to_one")
 
 
+class NullableUniqueTogetherModel(models.Model):
+    name = models.CharField(max_length=100)
+    field_1 = models.IntegerField(null=True)
+    field_2 = models.TextField(null=True)
+
+    class Meta:
+        unique_together = ("field_1", "field_2")
+
+
 class TestRelationalFieldMappings(TestCase):
     def test_pk_relations(self):
         class TestSerializer(serializers.ModelSerializer):
@@ -731,6 +740,17 @@ class TestRelationalFieldMappings(TestCase):
         """)
         self.assertEqual(repr(TestSerializer()), expected)
 
+    def test_nullable_unique_together(self):
+        class TestSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = NullableUniqueTogetherModel
+                fields = ('name', 'field_1', 'field_2')
+
+        serializer = TestSerializer(data={"name": "Test"})
+        self.assertTrue(serializer.is_valid(), serializer.errors)
+        instance = serializer.save()
+        assert isinstance(instance, NullableUniqueTogetherModel)
+
 
 class DisplayValueTargetModel(models.Model):
     name = models.CharField(max_length=100)
@@ -1402,14 +1422,10 @@ class Issue6751Test(TestCase):
         self.assertEqual(instance.char_field, 'value changed by signal')
 
 
-class Tag(models.Model):
+class UniqueConstraintNullableModel(models.Model):
-    name = models.CharField(max_length=100)
-
-
-class UniqueConstraintModel(models.Model):
     title = models.CharField(max_length=100)
     age = models.IntegerField(null=True)
-    tag = models.ForeignKey(Tag, on_delete=models.CASCADE, related_name='instances', null=True)
+    tag = models.CharField(max_length=100, null=True)
 
     class Meta:
         constraints = [
@@ -1420,12 +1436,12 @@ class UniqueConstraintModel(models.Model):
 
 class TestUniqueConstraintWithNullableFields(TestCase):
     def test_nullable_unique_constraint_fields_are_not_required(self):
-        class UniqueConstraintSerializer(serializers.ModelSerializer):
+        class UniqueConstraintNullableSerializer(serializers.ModelSerializer):
             class Meta:
-                model = UniqueConstraintModel
+                model = UniqueConstraintNullableModel
-                fields = '__all__'
+                fields = ('title', 'age', 'tag')
 
-        serializer = UniqueConstraintSerializer(data={'title': 'Bob'})
+        serializer = UniqueConstraintNullableSerializer(data={'title': 'Bob'})
         self.assertTrue(serializer.is_valid(), serializer.errors)
         result = serializer.save()
-        self.assertIsInstance(result, UniqueConstraintModel)
+        self.assertIsInstance(result, UniqueConstraintNullableModel)