Improved assert_serializer test assertions in test.serializers.

tests/serializers/test_data.py

@@ -10,6 +10,7 @@ forward, backwards and self references.
 import datetime
 import decimal
 import uuid
+from collections import namedtuple
 
 from django.core import serializers
 from django.db import connection, models
@@ -239,22 +240,22 @@ def inherited_compare(testcase, pk, klass, data):
         testcase.assertEqual(value, getattr(instance, key))
 
 
-# Define some data types. Each data type is
-# actually a pair of functions; one to create
-# and one to compare objects of that type
-data_obj = (data_create, data_compare)
-generic_obj = (generic_create, generic_compare)
-fk_obj = (fk_create, fk_compare)
-m2m_obj = (m2m_create, m2m_compare)
-im2m_obj = (im2m_create, im2m_compare)
-im_obj = (im_create, im_compare)
-o2o_obj = (o2o_create, o2o_compare)
-pk_obj = (pk_create, pk_compare)
-inherited_obj = (inherited_create, inherited_compare)
+# Define some test helpers. Each has a pair of functions: one to create objects and one
+# to make assertions against objects of a particular type.
+TestHelper = namedtuple("TestHelper", ["create_object", "compare_object"])
+data_obj = TestHelper(data_create, data_compare)
+generic_obj = TestHelper(generic_create, generic_compare)
+fk_obj = TestHelper(fk_create, fk_compare)
+m2m_obj = TestHelper(m2m_create, m2m_compare)
+im2m_obj = TestHelper(im2m_create, im2m_compare)
+im_obj = TestHelper(im_create, im_compare)
+o2o_obj = TestHelper(o2o_create, o2o_compare)
+pk_obj = TestHelper(pk_create, pk_compare)
+inherited_obj = TestHelper(inherited_create, inherited_compare)
 uuid_obj = uuid.uuid4()
 
 test_data = [
-    # Format: (data type, PK value, Model Class, data)
+    # Format: (test helper, PK value, Model Class, data)
     (data_obj, 1, BinaryData, memoryview(b"\x05\xFD\x00")),
     (data_obj, 5, BooleanData, True),
     (data_obj, 6, BooleanData, False),
@@ -410,35 +411,36 @@ class SerializerDataTests(TestCase):
 
 
 def assert_serializer(self, format, data):
-    # Create all the objects defined in the test data
+    # Create all the objects defined in the test data.
     objects = []
-    instance_count = {}
-    for func, pk, klass, datum in test_data:
+    for test_helper, pk, model, data_value in data:
         with connection.constraint_checks_disabled():
-            objects.extend(func[0](pk, klass, datum))
+            objects.extend(test_helper.create_object(pk, model, data_value))
 
-    # Get a count of the number of objects created for each class
-    for klass in instance_count:
-        instance_count[klass] = klass.objects.count()
+    # Get a count of the number of objects created for each model class.
+    instance_counts = {}
+    for _, _, model, _ in data:
+        if model not in instance_counts:
+            instance_counts[model] = model.objects.count()
 
-    # Add the generic tagged objects to the object list
+    # Add the generic tagged objects to the object list.
     objects.extend(Tag.objects.all())
 
-    # Serialize the test database
+    # Serialize the test database.
     serialized_data = serializers.serialize(format, objects, indent=2)
 
     for obj in serializers.deserialize(format, serialized_data):
         obj.save()
 
-    # Assert that the deserialized data is the same
-    # as the original source
-    for func, pk, klass, datum in test_data:
-        func[1](self, pk, klass, datum)
+    # Assert that the deserialized data is the same as the original source.
+    for test_helper, pk, model, data_value in data:
+        with self.subTest(model=model, data_value=data_value):
+            test_helper.compare_object(self, pk, model, data_value)
 
-    # Assert that the number of objects deserialized is the
-    # same as the number that was serialized.
-    for klass, count in instance_count.items():
-        self.assertEqual(count, klass.objects.count())
+    # Assert no new objects were created.
+    for model, count in instance_counts.items():
+        with self.subTest(model=model, count=count):
+            self.assertEqual(count, model.objects.count())
 
 
 def serializerTest(self, format):