fix formatting issues for list serializer validation fix

tests/test_serializer.py

@@ -2,6 +2,7 @@ import inspect
 import pickle
 import re
 import sys
+import unittest
 from collections import ChainMap
 from collections.abc import Mapping
 
@@ -10,7 +11,6 @@ from django.db import models
 
 from rest_framework import exceptions, fields, relations, serializers
 from rest_framework.fields import Field
-
 from .models import (
     ForeignKeyTarget, NestedForeignKeySource, NullableForeignKeySource
 )
@@ -787,9 +787,6 @@ class MyClassSerializer(serializers.ModelSerializer):
         return value
 
 
-import unittest
-
-
 class TestMultipleObjectsValidation(unittest.TestCase):
     def setUp(self):
         self.objs = [
@@ -818,7 +815,7 @@ class TestMultipleObjectsValidation(unittest.TestCase):
     def test_exception_raised_when_data_and_instance_length_different(self):
 
         with self.assertRaises(AssertionError):
-            serializer = MyClassSerializer(
+            MyClassSerializer(
                 data=[{'value': 'set', 'id': instance.id} for instance in
                       self.objs],
                 instance=self.objs[:-1],