LTI additional Python tests. LTI must use HTTPS for lis_outcome_service_url.

BLD-564.

CHANGELOG.rst

@@ -5,13 +5,15 @@ These are notable changes in edx-platform.  This is a rolling list of changes,
 in roughly chronological order, most recent first.  Add your entries at or near
 the top.  Include a label indicating the component affected.
 
+Blades: LTI additional Python tests. LTI must use HTTPS for
+lis_outcome_service_url. BLD-564.
+
 Blades: Fix bug when Image mapping problems are not working for students in IE. BLD-413.
 
 Blades: Add template that displays the most up-to-date features of
 drag-and-drop. BLD-479.
 
-Blades: LTI additional Python tests. LTI fix bug e-reader error when popping
-out window. BLD-465.
+Blades: LTI fix bug e-reader error when popping out window. BLD-465.
 
 Common: Switch from mitx.db to edx.db for sqlite databases. This will effectively
   reset state for local instances of the code, unless you manually rename your

common/lib/xmodule/xmodule/lti_module.py

@@ -259,37 +259,22 @@ class LTIModule(LTIFields, XModule):
             'element_class': self.category,
             'open_in_a_new_page': self.open_in_a_new_page,
             'display_name': self.display_name,
-            'form_url': self.get_form_path(),
+            'form_url': self.runtime.handler_url(self, 'preview_handler').rstrip('/?'),
         }
 
-
-    def get_form_path(self):
-        return  self.runtime.handler_url(self, 'preview_handler').rstrip('/?')
-
     def get_html(self):
         """
         Renders parameters to template.
         """
         return self.system.render_template('lti.html', self.get_context())
 
-    def get_form(self):
-        """
-        Renders parameters to form template.
-        """
-        return self.system.render_template('lti_form.html', self.get_context())
-
     @XBlock.handler
-    def preview_handler(self, request, dispatch):
+    def preview_handler(self, _, __):
         """
-        Ajax handler.
-
-        Args:
-            dispatch: string request slug
-
-        Returns:
-            json string
+        This is called to get context with new oauth params to iframe.
         """
-        return Response(self.get_form(), content_type='text/html')
+        template = self.system.render_template('lti_form.html', self.get_context())
+        return Response(template, content_type='text/html')
 
     def get_user_id(self):
         user_id = self.runtime.anonymous_student_id
@@ -299,8 +284,15 @@ class LTIModule(LTIFields, XModule):
     def get_outcome_service_url(self):
         """
         Return URL for storing grades.
+
+        To test LTI on sandbox we must use http scheme.
+
+        While testing locally and on Jenkins, mock_lti_server use http.referer
+        to obtain scheme, so it is ok to have http(s) anyway.
         """
-        uri = 'http://{host}{path}'.format(
+        scheme = 'http' if 'sandbox' in self.system.hostname else 'https'
+        uri = '{scheme}://{host}{path}'.format(
+            scheme=scheme,
             host=self.system.hostname,
             path=self.runtime.handler_url(self, 'grade_handler', thirdparty=True).rstrip('/?')
         )
@@ -449,7 +441,7 @@ oauth_consumer_key="", oauth_signature="frVp4JuvT1mVXlxktiAUjQ7%2F1cw%3D"'}
 
         Example of correct/incorrect answer XML body:: see response_xml_template.
         """
-        response_xml_template = textwrap.dedent("""
+        response_xml_template = textwrap.dedent("""\
             <?xml version="1.0" encoding="UTF-8"?>
             <imsx_POXEnvelopeResponse xmlns = "http://www.imsglobal.org/services/ltiv1p1/xsd/imsoms_v1p0">
                 <imsx_POXHeader>
@@ -578,7 +570,7 @@ oauth_consumer_key="", oauth_signature="frVp4JuvT1mVXlxktiAUjQ7%2F1cw%3D"'}
 
         sha1 = hashlib.sha1()
         sha1.update(request.body)
-        oauth_body_hash = base64.b64encode(sha1.hexdigest())
+        oauth_body_hash = base64.b64encode(sha1.digest())
 
         oauth_params = signature.collect_parameters(headers=headers, exclude_oauth_signature=False)
         oauth_headers =dict(oauth_params)

common/lib/xmodule/xmodule/tests/test_lti_unit.py

@@ -2,14 +2,21 @@
 """Test for LTI Xmodule functional logic."""
 
 from mock import Mock, patch, PropertyMock
+import mock
 import textwrap
 import json
 from lxml import etree
+import json
 from webob.request import Request
 from copy import copy
+from collections import OrderedDict
 import urllib
+import oauthlib
+import hashlib
+import base64
+
 
-from xmodule.lti_module import LTIDescriptor
+from xmodule.lti_module import LTIDescriptor, LTIError
 
 from . import LogicTest
 
@@ -48,7 +55,6 @@ class LTIModuleTest(LogicTest):
                 </imsx_POXEnvelopeRequest>
             """)
         self.system.get_real_user = Mock()
-        self.xmodule.get_client_key_secret = Mock(return_value=('key', 'secret'))
         self.system.publish = Mock()
 
         self.user_id = self.xmodule.runtime.anonymous_student_id
@@ -96,6 +102,7 @@ class LTIModuleTest(LogicTest):
     def test_authorization_header_not_present(self):
         """
         Request has no Authorization header.
+
         This is an unknown service request, i.e., it is not a part of the original service specification.
         """
         request = Request(self.environ)
@@ -115,6 +122,7 @@ class LTIModuleTest(LogicTest):
     def test_authorization_header_empty(self):
         """
         Request Authorization header has no value.
+
         This is an unknown service request, i.e., it is not a part of the original service specification.
         """
         request = Request(self.environ)
@@ -128,7 +136,6 @@ class LTIModuleTest(LogicTest):
             'description': 'The request has failed.',
             'messageIdentifier': self.DEFAULTS['messageIdentifier'],
         }
-
         self.assertEqual(response.status_code, 200)
         self.assertDictEqual(expected_response, real_response)
 
@@ -147,7 +154,6 @@ class LTIModuleTest(LogicTest):
             'description': 'The request has failed.',
             'messageIdentifier': 'unknown',
         }
-
         self.assertEqual(response.status_code, 200)
         self.assertDictEqual(expected_response, real_response)
 
@@ -166,7 +172,6 @@ class LTIModuleTest(LogicTest):
             'description': 'The request has failed.',
             'messageIdentifier': 'unknown',
         }
-
         self.assertEqual(response.status_code, 200)
         self.assertDictEqual(expected_response, real_response)
 
@@ -186,7 +191,6 @@ class LTIModuleTest(LogicTest):
             'description': 'Target does not support the requested operation.',
             'messageIdentifier': self.DEFAULTS['messageIdentifier'],
         }
-
         self.assertEqual(response.status_code, 200)
         self.assertDictEqual(expected_response, real_response)
 
@@ -199,7 +203,6 @@ class LTIModuleTest(LogicTest):
         request = Request(self.environ)
         request.body = self.get_request_body()
         response = self.xmodule.grade_handler(request, '')
-        code_major, description, messageIdentifier, action = self.get_response_values(response)
         description_expected = 'Score for {sourcedId} is now {score}'.format(
                 sourcedId=self.DEFAULTS['sourcedId'],
                 score=self.DEFAULTS['grade'],
@@ -221,20 +224,13 @@ class LTIModuleTest(LogicTest):
         self.assertEqual(real_user_id, expected_user_id)
 
     def test_outcome_service_url(self):
-        expected_outcome_service_url = 'http://{host}{path}'.format(
+        expected_outcome_service_url = 'https://{host}{path}'.format(
                 host=self.xmodule.runtime.hostname,
                 path=self.xmodule.runtime.handler_url(self.xmodule, 'grade_handler', thirdparty=True).rstrip('/?')
             )
-
         real_outcome_service_url = self.xmodule.get_outcome_service_url()
         self.assertEqual(real_outcome_service_url, expected_outcome_service_url)
 
-    def test_get_form_path(self):
-        expected_form_path = self.xmodule.runtime.handler_url(self.xmodule, 'preview_handler').rstrip('/?')
-
-        real_form_path = self.xmodule.get_form_path()
-        self.assertEqual(real_form_path, expected_form_path)
-
     def test_resource_link_id(self):
         with patch('xmodule.lti_module.LTIModule.id', new_callable=PropertyMock) as mock_id:
             mock_id.return_value = self.module_id
@@ -242,7 +238,6 @@ class LTIModuleTest(LogicTest):
             real_resource_link_id = self.xmodule.get_resource_link_id()
             self.assertEqual(real_resource_link_id, expected_resource_link_id)
 
-
     def test_lis_result_sourcedid(self):
         with patch('xmodule.lti_module.LTIModule.id', new_callable=PropertyMock) as mock_id:
             mock_id.return_value = self.module_id
@@ -251,11 +246,127 @@ class LTIModuleTest(LogicTest):
             self.assertEqual(real_lis_result_sourcedid, expected_sourcedId)
 
 
-    def test_verify_oauth_body_sign(self):
-        pass
+    @patch('xmodule.course_module.CourseDescriptor.id_to_location')
+    def test_client_key_secret(self, test):
+        """
+        LTI module gets client key and secret provided.
+        """
+        #this adds lti passports to system
+        mocked_course = Mock(lti_passports = ['lti_id:test_client:test_secret'])
+        modulestore = Mock()
+        modulestore.get_item.return_value = mocked_course
+        runtime = Mock(modulestore=modulestore)
+        self.xmodule.descriptor.runtime = runtime
+        self.xmodule.lti_id = "lti_id"
+        key, secret = self.xmodule.get_client_key_secret()
+        expected = ('test_client', 'test_secret')
+        self.assertEqual(expected, (key, secret))
+
+    @patch('xmodule.course_module.CourseDescriptor.id_to_location')
+    def test_client_key_secret_not_provided(self, test):
+        """
+        LTI module attempts to get client key and secret provided in cms.
+
+        There are key and secret but not for specific LTI.
+        """
+
+        #this adds lti passports to system
+        mocked_course = Mock(lti_passports = ['test_id:test_client:test_secret'])
+        modulestore = Mock()
+        modulestore.get_item.return_value = mocked_course
+        runtime = Mock(modulestore=modulestore)
+        self.xmodule.descriptor.runtime = runtime
+        #set another lti_id
+        self.xmodule.lti_id = "another_lti_id"
+        key_secret = self.xmodule.get_client_key_secret()
+        expected = ('','')
+        self.assertEqual(expected, key_secret)
+
+    @patch('xmodule.course_module.CourseDescriptor.id_to_location')
+    def test_bad_client_key_secret(self, test):
+        """
+        LTI module attempts to get client key and secret provided in cms.
+
+        There are key and secret provided in wrong format.
+        """
+        #this adds lti passports to system
+        mocked_course = Mock(lti_passports = ['test_id_test_client_test_secret'])
+        modulestore = Mock()
+        modulestore.get_item.return_value = mocked_course
+        runtime = Mock(modulestore=modulestore)
+        self.xmodule.descriptor.runtime = runtime
+        self.xmodule.lti_id = 'lti_id'
+        with self.assertRaises(LTIError):
+            self.xmodule.get_client_key_secret()
+
+    @patch('xmodule.lti_module.signature.verify_hmac_sha1', return_value=True)
+    @patch('xmodule.lti_module.LTIModule.get_client_key_secret', return_value=('test_client_key', u'test_client_secret'))
+    def test_successful_verify_oauth_body_sign(self, get_key_secret, mocked_verify):
+        """
+        Test if OAuth signing was successful.
+        """
+        try:
+            self.xmodule.verify_oauth_body_sign(self.get_signed_grade_mock_request())
+        except LTIError:
+            self.fail("verify_oauth_body_sign() raised LTIError unexpectedly!")
+
+    @patch('xmodule.lti_module.signature.verify_hmac_sha1', return_value=False)
+    @patch('xmodule.lti_module.LTIModule.get_client_key_secret', return_value=('test_client_key', u'test_client_secret'))
+    def test_failed_verify_oauth_body_sign(self, get_key_secret, mocked_verify):
+        """
+        Oauth signing verify fail.
+        """
+        with self.assertRaises(LTIError):
+            req = self.get_signed_grade_mock_request()
+            self.xmodule.verify_oauth_body_sign(req)
+
+    def get_signed_grade_mock_request(self):
+        """
+        Example of signed request from LTI Provider.
+        """
+        mock_request = Mock()
+        mock_request.headers = {
+            'X-Requested-With': 'XMLHttpRequest',
+            'Content-Type': 'application/xml',
+            'Authorization': u'OAuth oauth_nonce="135685044251684026041377608307", \
+                oauth_timestamp="1234567890", oauth_version="1.0", \
+                oauth_signature_method="HMAC-SHA1", \
+                oauth_consumer_key="test_client_key", \
+                oauth_signature="my_signature%3D", \
+                oauth_body_hash="gz+PeJZuF2//n9hNUnDj2v5kN70="'
+        }
+        mock_request.url = u'http://testurl'
+        mock_request.http_method = u'POST'
+        mock_request.body = textwrap.dedent("""
+            <?xml version = "1.0" encoding = "UTF-8"?>
+                <imsx_POXEnvelopeRequest  xmlns="http://www.imsglobal.org/services/ltiv1p1/xsd/imsoms_v1p0">
+                </imsx_POXEnvelopeRequest>
+        """)
+        return mock_request
+
+    def test_good_custom_params(self):
+        """
+        Custom parameters are presented in right format.
+        """
+        self.xmodule.custom_parameters = ['test_custom_params=test_custom_param_value']
+        self.xmodule.get_client_key_secret = Mock(return_value=('test_client_key', 'test_client_secret'))
+        self.xmodule.oauth_params = Mock()
+        self.xmodule.get_input_fields()
+        self.xmodule.oauth_params.assert_called_with(
+            {u'custom_test_custom_params': u'test_custom_param_value'},
+            'test_client_key', 'test_client_secret'
+        )
 
-    def test_client_key_secret(self):
-        pass
+    def test_bad_custom_params(self):
+        """
+        Custom parameters are presented in wrong format.
+        """
+        bad_custom_params = ['test_custom_params: test_custom_param_value']
+        self.xmodule.custom_parameters = bad_custom_params
+        self.xmodule.get_client_key_secret = Mock(return_value=('test_client_key', 'test_client_secret'))
+        self.xmodule.oauth_params = Mock()
+        with self.assertRaises(LTIError):
+            self.xmodule.get_input_fields()
 
     def test_max_score(self):
         self.xmodule.weight = 100.0

lms/djangoapps/courseware/features/lti_setup.py

@@ -38,6 +38,10 @@ def setup_mock_lti_server():
         'lti_endpoint': 'correct_lti_endpoint'
     }
 
+    # Flag for acceptance tests used for creating right callback_url and sending
+    # graded result. Used in MockLTIRequestHandler.
+    server.test_mode = True
+
     # Store the server instance in lettuce's world
     # so that other steps can access it
     # (and we can shut it down later)

lms/djangoapps/courseware/mock_lti_server/mock_lti_server.py

+"""
+LTI Server
+
+What is supported:
+------------------
+
+1.) This LTI Provider can service only one Tool Consumer at the same time. It is
+not possible to have this LTI multiple times on a single page in LMS.
+
+"""
 from BaseHTTPServer import HTTPServer, BaseHTTPRequestHandler
 from uuid import uuid4
 import textwrap
@@ -23,6 +33,7 @@ class MockLTIRequestHandler(BaseHTTPRequestHandler):
     protocol = "HTTP/1.0"
     callback_url = None
 
+
     def log_message(self, format, *args):
         """Log an arbitrary message."""
         # Code copied from BaseHTTPServer.py. Changed to write to sys.stdout
@@ -35,6 +46,8 @@ class MockLTIRequestHandler(BaseHTTPRequestHandler):
     def do_GET(self):
         '''
         Handle a GET request from the client and sends response back.
+
+        Used for checking LTI Provider started correctly.
         '''
 
         self.send_response(200, 'OK')
@@ -42,29 +55,20 @@ class MockLTIRequestHandler(BaseHTTPRequestHandler):
         self.end_headers()
 
         response_str = """<html><head><title>TEST TITLE</title></head>
-            <body>I have stored grades.</body></html>"""
+            <body>This is LTI Provider.</body></html>"""
 
         self.wfile.write(response_str)
 
-        self._send_graded_result()
-
 
 
     def do_POST(self):
         '''
         Handle a POST request from the client and sends response back.
         '''
-
-        '''
-        logger.debug("LTI provider received POST request {} to path {}".format(
-            str(self.post_dict),
-            self.path)
-        )  # Log the request
-        '''
-        # Respond to grade request
         if 'grade' in self.path and self._send_graded_result().status_code == 200:
             status_message = 'LTI consumer (edX) responded with XML content:<br>' + self.server.grade_data['TC answer']
             self.server.grade_data['callback_url'] = None
+            self._send_response(status_message, 200)
         # Respond to request with correct lti endpoint:
         elif self._is_correct_lti_request():
             self.post_dict = self._post_dict()
@@ -97,26 +101,19 @@ class MockLTIRequestHandler(BaseHTTPRequestHandler):
             # set data for grades
             # what need to be stored as server data
             self.server.grade_data = {
-                'callback_url': self.post_dict["lis_outcome_service_url"],
-                'sourcedId': self.post_dict['lis_result_sourcedid']
+                'callback_url': self.post_dict.get('lis_outcome_service_url'),
+                'sourcedId': self.post_dict.get('lis_result_sourcedid')
             }
+            self._send_response(status_message, 200)
         else:
             status_message = "Invalid request URL"
+            self._send_response(status_message, 500)
 
-        self._send_head()
-        self._send_response(status_message)
-
-    def _send_head(self):
+    def _send_head(self, status_code):
         '''
         Send the response code and MIME headers
         '''
-        self.send_response(200)
-        '''
-        if self._is_correct_lti_request():
-            self.send_response(200)
-        else:
-            self.send_response(500)
-        '''
+        self.send_response(status_code)
         self.send_header('Content-type', 'text/html')
         self.end_headers()
 
@@ -182,15 +179,22 @@ class MockLTIRequestHandler(BaseHTTPRequestHandler):
                 </imsx_POXEnvelopeRequest>
         """)
         data = payload.format(**values)
-        # temporarily changed to get for easy view in browser
         # get relative part, because host name is different in a) manual tests b) acceptance tests c) demos
+        if getattr(self.server, 'test_mode', None):
             relative_url = urlparse.urlparse(self.server.grade_data['callback_url']).path
             url = self.server.referer_host + relative_url
+        else:
+            url = self.server.grade_data['callback_url']
 
         headers = {'Content-Type': 'application/xml', 'X-Requested-With': 'XMLHttpRequest'}
-
         headers['Authorization'] = self.oauth_sign(url, data)
 
+        # We can't mock requests in unit tests, because we use them, but we need
+        # them to be mocked only for this one case.
+        if getattr(self.server, 'run_inside_unittest_flag', None):
+            response = mock.Mock(status_code=200, url=url, data=data, headers=headers)
+            return response
+
         response = requests.post(
             url,
             data=data,
@@ -199,11 +203,11 @@ class MockLTIRequestHandler(BaseHTTPRequestHandler):
         self.server.grade_data['TC answer'] = response.content
         return response
 
-    def _send_response(self, message):
+    def _send_response(self, message, status_code):
         '''
         Send message back to the client
         '''
-
+        self._send_head(status_code)
         if self.server.grade_data['callback_url']:
             response_str = """<html><head><title>TEST TITLE</title></head>
                 <body>
@@ -250,7 +254,7 @@ class MockLTIRequestHandler(BaseHTTPRequestHandler):
         #Calculate and encode body hash. See http://oauth.googlecode.com/svn/spec/ext/body_hash/1.0/oauth-bodyhash.html
         sha1 = hashlib.sha1()
         sha1.update(body)
-        oauth_body_hash = base64.b64encode(sha1.hexdigest())
+        oauth_body_hash = base64.b64encode(sha1.digest())
         __, headers, __ = client.sign(
             unicode(url.strip()),
             http_method=u'POST',

lms/djangoapps/courseware/mock_lti_server/server_start.py

 """
 Mock LTI server for manual testing.
+
+Used for manual testing and testing on sandbox.
 """
 
 import threading
@@ -18,6 +20,10 @@ server.oauth_settings = {
 }
 server.server_host = server_host
 
+# If in test mode mock lti server will make callback url using referer host.
+# Used in MockLTIRequestHandler when sending graded result.
+server.test_mode = True
+
 try:
     server.serve_forever()
 except KeyboardInterrupt:

lms/djangoapps/courseware/mock_lti_server/test_mock_lti_server.py

@@ -11,7 +11,6 @@ import requests
 from mock_lti_server import MockLTIServer
 
 
-
 class MockLTIServerTest(unittest.TestCase):
     '''
     A mock version of the LTI provider server that listens on a local
@@ -33,6 +32,10 @@ class MockLTIServerTest(unittest.TestCase):
             'lti_base':  'http://{}:{}/'.format(server_host, server_port),
             'lti_endpoint': 'correct_lti_endpoint'
         }
+        self.server.run_inside_unittest_flag = True
+        #flag for creating right callback_url
+        self.server.test_mode = True
+
         # Start the server in a separate daemon thread
         server_thread = threading.Thread(target=self.server.serve_forever)
         server_thread.daemon = True
@@ -43,6 +46,24 @@ class MockLTIServerTest(unittest.TestCase):
         # Stop the server, freeing up the port
         self.server.shutdown()
 
+
+    def test_wrong_header(self):
+        """
+        Tests that LTI server processes request with right program
+        path and responses with wrong header.
+        """
+        #wrong number of params
+        payload = {
+            'user_id': 'default_user_id',
+            'role': 'student',
+            'oauth_nonce': '',
+            'oauth_timestamp': '',
+        }
+        uri = self.server.oauth_settings['lti_base'] + self.server.oauth_settings['lti_endpoint']
+        headers = {'referer': 'http://localhost:8000/'}
+        response = requests.post(uri, data=payload, headers=headers)
+        self.assertIn('Incorrect LTI header', response.content)
+
     def test_wrong_signature(self):
         """
         Tests that LTI server processes request with right program
@@ -65,19 +86,16 @@ class MockLTIServerTest(unittest.TestCase):
             'lis_result_sourcedid': '',
             'resource_link_id':'',
         }
-
         uri = self.server.oauth_settings['lti_base'] + self.server.oauth_settings['lti_endpoint']
         headers = {'referer': 'http://localhost:8000/'}
         response = requests.post(uri, data=payload, headers=headers)
-
-        self.assertTrue('Wrong LTI signature' in response.content)
+        self.assertIn('Wrong LTI signature', response.content)
 
 
     def test_success_response_launch_lti(self):
         """
         Success lti launch.
         """
-
         payload = {
             'user_id': 'default_user_id',
             'role': 'student',
@@ -100,8 +118,40 @@ class MockLTIServerTest(unittest.TestCase):
 
         uri = self.server.oauth_settings['lti_base'] + self.server.oauth_settings['lti_endpoint']
         headers = {'referer': 'http://localhost:8000/'}
+        response = requests.post(uri, data=payload, headers=headers)
+        self.assertIn('This is LTI tool. Success.', response.content)
+
+    def test_send_graded_result(self):
 
+        payload = {
+            'user_id': 'default_user_id',
+            'role': 'student',
+            'oauth_nonce': '',
+            'oauth_timestamp': '',
+            'oauth_consumer_key': 'client_key',
+            'lti_version': 'LTI-1p0',
+            'oauth_signature_method': 'HMAC-SHA1',
+            'oauth_version': '1.0',
+            'oauth_signature': '',
+            'lti_message_type': 'basic-lti-launch-request',
+            'oauth_callback': 'about:blank',
+            'launch_presentation_return_url': '',
+            'lis_outcome_service_url': '',
+            'lis_result_sourcedid': '',
+            'resource_link_id':'',
+            "lis_outcome_service_url": '',
+        }
+        self.server.check_oauth_signature = Mock(return_value=True)
+
+        uri = self.server.oauth_settings['lti_base'] + self.server.oauth_settings['lti_endpoint']
+        #this is the uri for sending grade from lti
+        headers = {'referer': 'http://localhost:8000/'}
         response = requests.post(uri, data=payload, headers=headers)
 
         self.assertTrue('This is LTI tool. Success.' in response.content)
+        self.server.grade_data['TC answer'] = "Test response"
+        graded_response = requests.post('http://127.0.0.1:8034/grade')
+        self.assertIn('Test response', graded_response.content)
+
+
 

lms/djangoapps/courseware/tests/test_lti_integration.py

@@ -33,7 +33,7 @@ class TestLTI(BaseTestXmodule):
 
         sourcedId = u':'.join(urllib.quote(i) for i in (lti_id, module_id, user_id))
 
-        lis_outcome_service_url = 'http://{host}{path}'.format(
+        lis_outcome_service_url = 'https://{host}{path}'.format(
                 host=self.item_descriptor.xmodule_runtime.hostname,
                 path=self.item_descriptor.xmodule_runtime.handler_url(self.item_module, 'grade_handler', thirdparty=True).rstrip('/?')
             )
@@ -59,6 +59,16 @@ class TestLTI(BaseTestXmodule):
 
         saved_sign = oauthlib.oauth1.Client.sign
 
+        self.expected_context = {
+            'display_name': self.item_module.display_name,
+            'input_fields': self.correct_headers,
+            'element_class': self.item_module.category,
+            'element_id': self.item_module.location.html_id(),
+            'launch_url': 'http://www.example.com',  # default value
+            'open_in_a_new_page': True,
+            'form_url': self.item_descriptor.xmodule_runtime.handler_url(self.item_module, 'preview_handler').rstrip('/?'),
+        }
+
         def mocked_sign(self, *args, **kwargs):
             """
             Mocked oauth1 sign function.
@@ -79,21 +89,11 @@ class TestLTI(BaseTestXmodule):
         self.addCleanup(patcher.stop)
 
     def test_lti_constructor(self):
-        """
-        Makes sure that all parameters extracted.
-        """
-        generated_context = self.item_module.render('student_view').content
-        expected_context = {
-            'display_name': self.item_module.display_name,
-            'input_fields': self.correct_headers,
-            'element_class': self.item_module.category,
-            'element_id': self.item_module.location.html_id(),
-            'launch_url': 'http://www.example.com',  # default value
-            'open_in_a_new_page': True,
-            'form_url': self.item_descriptor.xmodule_runtime.handler_url(self.item_module, 'preview_handler').rstrip('/?'),
-        }
+        generated_content = self.item_module.render('student_view').content
+        expected_content =  self.runtime.render_template('lti.html', self.expected_context)
+        self.assertEqual(generated_content, expected_content)
 
-        self.assertEqual(
-            generated_context,
-            self.runtime.render_template('lti.html', expected_context),
-        )
+    def test_lti_preview_handler(self):
+        generated_content = self.item_module.preview_handler(None, None).body
+        expected_content = self.runtime.render_template('lti_form.html', self.expected_context)
+        self.assertEqual(generated_content, expected_content)