Ignore known error codes from the rostering services

We'll tackle this individually as we gather more information are able to
reproduce and fix them.

lms/services/roster.py

@@ -119,24 +119,13 @@ def fetch_assignment_roster(self, assignment: Assignment) -> None:
                 resource_link_id=assignment.lti_v13_resource_link_id,
             )
         except ExternalRequestError as err:
-            if (
-                err.response_body
-                and (
-                    # Error message from Canvas
-                    "Requested ResourceLink bound to unexpected external tool"
-                    in err.response_body
-                )
-                # In cases for which we have different assignment IDs
-                and assignment.resource_link_id != assignment.lti_v13_resource_link_id
+            if err.response_body and (
+                "Requested ResourceLink bound to unexpected external tool"  # Canvas, unknown reason
+                in err.response_body
             ):
-                # The LMS (Canvas) doesn't seem to be able to link our tool to this assignment
-                # Try the same call but with the LTI1.1 assignment identifier.
-                LOG.info("Try to fetch roster with the LTI1.1 identifier")
-                roster = self._lti_names_roles_service.get_context_memberships(
-                    lti_registration,
-                    lms_course.lti_context_memberships_url,
-                    resource_link_id=assignment.resource_link_id,
-                )
+                LOG.error("Fetching assignment roster failed: %s", err.response_body)
+                # We ignore this type of error, just stop here.
+                return
             else:
                 raise
 

tests/unit/lms/services/roster_test.py

@@ -128,45 +128,19 @@ def test_fetch_assignment_roster(
         assert not roster[3].active
 
     def test_fetch_assignment_roster_retries_with_lti_v11_id(
-        self,
-        svc,
-        lti_names_roles_service,
-        lti_v13_application_instance,
-        assignment,
-        names_and_roles_roster_response,
-        lti_role_service,
+        self, svc, lti_names_roles_service, assignment
     ):
-        lti_role_service.get_roles.return_value = [
-            factories.LTIRole(value="ROLE1"),
-            factories.LTIRole(value="ROLE2"),
-        ]
-
-        lti_names_roles_service.get_context_memberships.side_effect = [
+        lti_names_roles_service.get_context_memberships.side_effect = (
             ExternalRequestError(
                 response=Mock(
                     text="Requested ResourceLink bound to unexpected external tool"
                 )
-            ),
-            names_and_roles_roster_response,
-        ]
-
-        svc.fetch_assignment_roster(assignment)
-
-        lti_names_roles_service.get_context_memberships.assert_has_calls(
-            [
-                call(
-                    lti_v13_application_instance.lti_registration,
-                    "SERVICE_URL",
-                    assignment.lti_v13_resource_link_id,
-                ),
-                call(
-                    lti_v13_application_instance.lti_registration,
-                    "SERVICE_URL",
-                    assignment.resource_link_id,
-                ),
-            ]
+            )
         )
 
+        # Method finishes without re-raising the exception
+        assert not svc.fetch_assignment_roster(assignment)
+
     def test_fetch_assignment_roster_raises_external_request_error(
         self, svc, lti_names_roles_service, assignment
     ):