'Perform the modulestore-building and course creation steps for a mixed modulestore test.'

@contextmanager
def _build_store(self, default_ms):

    with MongoContentstoreBuilder().build() as contentstore:
        self._initialize_mixed(contentstore=contentstore, mappings={})
        with self.store.default_store(default_ms):
            source_course_key = self.store.make_course_key('org.source', 'course.source', 'run.source')
            self._create_course(source_course_key)
            (yield (contentstore, source_course_key))
