test: switch default test store to the split store

It's long past time that the default test modulestore was Split,
instead of Old Mongo. This commit switches the default store and
fixes some tests that now fail:
- Tests that didn't expect MFE to be enabled (because we don't
  enable MFE for Old Mongo) - opt out of MFE for those
- Tests that hardcoded old key string formats
- Lots of other random little differences

In many places, I didn't spend much time trying to figure out how to
properly fix the test, and instead just set the modulestore to Old
Mongo.

For those tests that I didn't spend time investigating, I've set
the modulestore to TEST_DATA_MONGO_AMNESTY_MODULESTORE - search for
that string to find further work.

lms/djangoapps/mobile_api/testutils.py

@@ -22,6 +22,8 @@ from django.urls import reverse
 from django.utils import timezone
 from opaque_keys.edx.keys import CourseKey
 from rest_framework.test import APITestCase
+from xmodule.modulestore.tests.django_utils import TEST_DATA_MONGO_AMNESTY_MODULESTORE, ModuleStoreTestCase
+from xmodule.modulestore.tests.factories import CourseFactory
 
 from common.djangoapps.student import auth
 from common.djangoapps.student.models import CourseEnrollment
@@ -30,8 +32,6 @@ from lms.djangoapps.courseware.access_response import MobileAvailabilityError, S
 from lms.djangoapps.mobile_api.models import IgnoreMobileAvailableFlagConfig
 from lms.djangoapps.mobile_api.tests.test_milestones import MobileAPIMilestonesMixin
 from lms.djangoapps.mobile_api.utils import API_V1
-from xmodule.modulestore.tests.django_utils import ModuleStoreTestCase  # lint-amnesty, pylint: disable=wrong-import-order
-from xmodule.modulestore.tests.factories import CourseFactory  # lint-amnesty, pylint: disable=wrong-import-order
 
 
 class MobileAPITestCase(ModuleStoreTestCase, APITestCase):
@@ -41,6 +41,8 @@ class MobileAPITestCase(ModuleStoreTestCase, APITestCase):
        REVERSE_INFO = {'name': <django reverse name>, 'params': [<list of params in the URL>]}
     They may also override any of the methods defined in this class to control the behavior of the TestMixins.
     """
+    MODULESTORE = TEST_DATA_MONGO_AMNESTY_MODULESTORE
+
     def setUp(self):
         super().setUp()
         self.course = CourseFactory.create(
@@ -172,7 +174,7 @@ class MobileCourseAccessTestMixin(MobileAPIMilestonesMixin):
         self.verify_success(response)  # allow subclasses to override verification
 
     def test_course_not_found(self):
-        non_existent_course_id = CourseKey.from_string('a/b/c')
+        non_existent_course_id = CourseKey.from_string('course-v1:a+b+c')
         self.init_course_access(course_id=non_existent_course_id)
 
         response = self.api_response(expected_response_code=None, course_id=non_existent_course_id)
@@ -205,7 +207,7 @@ class MobileCourseAccessTestMixin(MobileAPIMilestonesMixin):
         self.init_course_access()
         # set mobile_available to False for the test course
         self.course.mobile_available = False
-        self.store.update_item(self.course, self.user.id)
+        self.course = self.update_course(self.course, self.user.id)
         self._verify_response(should_succeed, MobileAvailabilityError(), role)
 
         IgnoreMobileAvailableFlagConfig(enabled=True).save()
@@ -226,7 +228,7 @@ class MobileCourseAccessTestMixin(MobileAPIMilestonesMixin):
     def test_visible_to_staff_only_course(self, role, should_succeed):
         self.init_course_access()
         self.course.visible_to_staff_only = True
-        self.store.update_item(self.course, self.user.id)
+        self.course = self.update_course(self.course, self.user.id)
         if self.ALLOW_ACCESS_TO_NON_VISIBLE_COURSE:
             should_succeed = True
         self._verify_response(should_succeed, VisibilityError(), role)

lms/djangoapps/mobile_api/users/tests.py

@@ -645,7 +645,7 @@ class TestCourseEnrollmentSerializer(MobileAPITestCase, MilestonesTestCaseMixin)
     def test_with_display_overrides(self, api_version):
         self.course.display_coursenumber = "overridden_number"
         self.course.display_organization = "overridden_org"
-        self.store.update_item(self.course, self.user.id)
+        self.course = self.update_course(self.course, self.user.id)
 
         serialized = self.get_serialized_data(api_version)
         assert serialized['course']['number'] == self.course.display_coursenumber