Fix linking problem for peer grading, add in a test

Conflicts:
	common/lib/xmodule/xmodule/tests/test_peer_grading.py

common/lib/xmodule/xmodule/peer_grading_module.py

@@ -72,6 +72,12 @@ class PeerGradingFields(object):
         scope=Scope.content
     )
 
+class InvalidLinkLocation(Exception):
+    """
+    Exception for the case in which a peer grading module tries to link to an invalid location.
+    """
+    pass
+
 
 class PeerGradingModule(PeerGradingFields, XModule):
     """
@@ -103,7 +109,13 @@ class PeerGradingModule(PeerGradingFields, XModule):
 
         if self.use_for_single_location:
             try:
-                self.linked_problem = self.system.get_module(self.link_to_location)
+                linked_descriptors = self.descriptor.get_required_module_descriptors()
+                if len(linked_descriptors) == 0:
+                    error_msg = "Peer grading module {0} is trying to use single problem mode without "
+                    "a location specified.".format(self.location)
+                    log.error(error_msg)
+                    raise InvalidLinkLocation(error_msg)
+                self.linked_problem = self.system.get_module(linked_descriptors[0])
             except ItemNotFoundError:
                 log.error("Linked location {0} for peer grading module {1} does not exist".format(
                     self.link_to_location, self.location))

common/lib/xmodule/xmodule/tests/test_peer_grading.py

@@ -4,6 +4,10 @@ from .import get_test_system
 from test_util_open_ended import MockQueryDict, DummyModulestore
 from xmodule.open_ended_grading_classes.peer_grading_service import MockPeerGradingService
 import json
+from mock import Mock
+from xmodule.peer_grading_module import PeerGradingModule
+from xblock.field_data import DictFieldData
+from xblock.fields import ScopeIds
 
 import logging
 
@@ -180,4 +184,54 @@ class PeerGradingModuleScoredTest(unittest.TestCase, DummyModulestore):
         # Swap for our mock class, which will find peer grading.
         peer_grading.peer_gs = MockPeerGradingServiceProblemList()
         html = peer_grading.peer_grading()
-        self.assertIn("Peer-Graded", html)
\ No newline at end of file
+        self.assertIn("Peer-Graded", html)
+
+class PeerGradingModuleLinkedTest(unittest.TestCase, DummyModulestore):
+    """
+    Test peer grading that is linked to an open ended module.
+    """
+    problem_location = Location(["i4x", "edX", "open_ended", "peergrading",
+                                 "PeerGradingLinked"])
+    coe_location = Location(["i4x", "edX", "open_ended", "combinedopenended",
+                             "SampleQuestion"])
+
+    def setUp(self):
+        """
+        Create a peer grading module from a test system.
+        """
+        self.test_system = get_test_system()
+        self.test_system.open_ended_grading_interface = None
+        self.setup_modulestore(COURSE)
+
+    def test_linked_problem(self):
+        """
+        Check to see if a peer grading module with a linked problem loads properly.
+        """
+
+        # Mock the linked problem descriptor.
+        linked_descriptor = Mock()
+        linked_descriptor.location = self.coe_location
+
+        # Mock the peer grading descriptor.
+        pg_descriptor = Mock()
+        pg_descriptor.location = self.problem_location
+        pg_descriptor.get_required_module_descriptors = lambda: [linked_descriptor, ]
+
+        # Setup the proper field data for the peer grading module.
+        field_data = DictFieldData({
+            'data': '<peergrading/>',
+            'location': self.problem_location,
+            'use_for_single_location': True,
+            'link_to_location': self.coe_location,
+        })
+
+        # Initialize the peer grading module.
+        peer_grading = PeerGradingModule(
+            pg_descriptor,
+            self.test_system,
+            field_data,
+            ScopeIds(None, None, self.problem_location, self.problem_location)
+        )
+
+        # Ensure that it is properly setup.
+        self.assertTrue(peer_grading.use_for_single_location)

common/test/data/open_ended/course/2012_Fall.xml

@@ -4,5 +4,6 @@
     <combinedopenended url_name="SampleQuestion1Attempt"/>
     <peergrading url_name="PeerGradingSample"/>
     <peergrading url_name="PeerGradingScored"/>
+    <peergrading url_name="PeerGradingLinked"/>
   </chapter>
 </course>

common/test/data/open_ended/peergrading/PeerGradingLinked.xml

+<peergrading is_graded="True" max_grade="1" use_for_single_location="True" link_to_location="i4x://edX/open_ended/combinedopenended/SampleQuestion"/>
\ No newline at end of file