如何魔術模擬長鏈調用？

Question

為了測試以下功能，我想斷言.filter()使用參數filters調用一次。

def get_instances(session: boto3.session.Session, filters):
    instances = session.resource('ec2').instances.filter(Filters=filters)
    return instances

我試着寫單元測試，

def test_get_instance():
    mocked_session: boto3.session.Session = boto3.session.Session()

    def resource(service_name) -> boto3.resources.base.ServiceResource:
        if service_name == 'ec2':
            return MagicMock()
        raise Exception('Parameter should be ec2')

    mocked_session.resource = MagicMock(side_effect=resource)  # resource is set?
    mocked_session.resource('ec2').instances = MagicMock()
    # mocked_session.resource('ec2').instances. ??? # not finished

    filters = None
    Node.get_nodes(mocked_session, filters)
    assert session.resource('ec2').instances.filter.call_count == 1

但是，測試 function 得到以下錯誤

>       assert session.resource('ec2').instances.filter.call_count == 1
E       AttributeError: 'function' object has no attribute 'resource'

Answer 1

為此，您可以使用內置的monckeypatch固定裝置。

def test_get_instance(monkeypatch):
    # ... your code
    filter_calls = []
    monkeypatch.setattr(mocked_session.resource('ec2'), 'filter', lambda Filters: filter_calls.append(1))
    assert len(filter_calls) == 1

我沒有使用boto3庫對其進行測試，但是，想法就在這里。