'Assign `username` to `team_id`.'

def create_membership(self, username, team_id):

    response = self.course_fixture.session.post((LMS_BASE_URL + '/api/team/v0/team_membership/'), data=json.dumps({'username': username, 'team_id': team_id}), headers=self.course_fixture.headers)
    return json.loads(response.text)
