Tests for the commit_on_success_with_read_committed decorator.

TNL-367

common/djangoapps/util/tests/test_db.py

+"""Tests for util.db module."""
+
+import ddt
+import threading
+import time
+import unittest
+
+from django.contrib.auth.models import User
+from django.db import connection, IntegrityError
+from django.db.transaction import commit_on_success
+from django.test import TransactionTestCase
+
+from util.db import commit_on_success_with_read_committed
+
+
+@ddt.ddt
+class TransactionIsolationLevelsTestCase(TransactionTestCase):
+    """
+    Tests the effects of changing transaction isolation level to READ COMMITTED instead of REPEATABLE READ.
+
+    Note: This TestCase only works with MySQL.
+
+    To run it on devstack:
+    1. Add TEST_RUNNER = 'django_nose.NoseTestSuiteRunner' to envs/devstack.py
+    2. Run "./manage.py lms --settings=devstack test util.tests.test_db"
+    """
+
+    @ddt.data(
+        (commit_on_success, IntegrityError, None, True),
+        (commit_on_success_with_read_committed, type(None), False, True),
+    )
+    @ddt.unpack
+    def test_concurrent_requests(self, transaction_decorator, exception_class, created_in_1, created_in_2):
+        """
+        Test that when isolation level is set to READ COMMITTED get_or_create()
+        for the same row in concurrent requests does not raise an IntegrityError.
+        """
+
+        if connection.vendor != 'mysql':
+            raise unittest.SkipTest('Only works on MySQL.')
+
+        class RequestThread(threading.Thread):
+            """ A thread which runs a dummy view."""
+            def __init__(self, delay, **kwargs):
+                super(RequestThread, self).__init__(**kwargs)
+                self.delay = delay
+                self.status = {}
+
+            @transaction_decorator
+            def run(self):
+                """A dummy view."""
+                try:
+                    try:
+                        User.objects.get(username='student', email='student@edx.org')
+                    except User.DoesNotExist:
+                        pass
+                    else:
+                        raise AssertionError('Did not raise User.DoesNotExist.')
+
+                    if self.delay > 0:
+                        time.sleep(self.delay)
+
+                    __, created = User.objects.get_or_create(username='student', email='student@edx.org')
+                except Exception as exception:  # pylint: disable=broad-except
+                    self.status['exception'] = exception
+                else:
+                    self.status['created'] = created
+
+        thread1 = RequestThread(delay=1)
+        thread2 = RequestThread(delay=0)
+
+        thread1.start()
+        thread2.start()
+        thread2.join()
+        thread1.join()
+
+        self.assertIsInstance(thread1.status.get('exception'), exception_class)
+        self.assertEqual(thread1.status.get('created'), created_in_1)
+
+        self.assertIsNone(thread2.status.get('exception'))
+        self.assertEqual(thread2.status.get('created'), created_in_2)