async def METHOD_NAME(self):
    school = await testmodels.School.create(id=1024, name="School1")
    school2 = await testmodels.School.create(id=2048, name="School2")
    principal0 = await testmodels.Principal.create(name="Sang-Heon Jeon", school=school)
    await testmodels.Principal.filter(id=principal0.id).update(school=school2)
    principal = await testmodels.Principal.get(id=principal0.id)
    await principal.fetch_related("school")
    self.assertEqual(principal.school, school2)
    self.assertEqual(await school.principal, None)
    self.assertEqual(await school2.principal, principal)