Add tests for diango-comment-client middleware

lms/djangoapps/django_comment_client/tests/test_middleware.py

+import string
+import random
+import collections
+
+from django.test import TestCase                         
+
+import comment_client
+import django.http
+import django_comment_client.middleware as middleware
+
+class AjaxExceptionTestCase(TestCase):
+
+# TODO: check whether the correct error message is produced. 
+# The error message should be the same as the argument to CommentClientError
+	def setUp(self):
+		self.a = middleware.AjaxExceptionMiddleware()
+		self.request1 = django.http.HttpRequest()
+		self.request0 = django.http.HttpRequest()
+		self.exception1 = comment_client.CommentClientError('{}')
+		self.exception0 = ValueError()
+		self.request1.META['HTTP_X_REQUESTED_WITH'] = "XMLHttpRequest"
+		self.request0.META['HTTP_X_REQUESTED_WITH'] = "SHADOWFAX"
+		
+	def test_process_exception(self):
+		self.assertIsInstance(self.a.process_exception(self.request1, self.exception1), middleware.JsonError)
+		self.assertIsNone(self.a.process_exception(self.request1, self.exception0))
+		self.assertIsNone(self.a.process_exception(self.request0, self.exception1))
+		self.assertIsNone(self.a.process_exception(self.request0, self.exception0))