def test_start_after_join():
 group = worker.WalTransferGroup(FakeWalUploader())
 group.join()
 seg = FakeWalSegment('arbitrary')
 with pytest.raises(UserCritical):
  group.start(seg)

def test_start_after_join ( ) : group = worker . WalTransferGroup ( FakeWalUploader ( ) ) group . join ( ) seg = FakeWalSegment ( 'arbitrary' ) with pytest . raises ( UserCritical ) : group . start ( seg )
break an invariant by adding transfers after .