模拟python单元测试中的问题

我写了如下测试：

class TestLoader(TestCase):

@pytest.fixture(autouse=True)
@patch('loaders.myloader.DSFactory')
def _initialize_(self, mock_ds_factory):
    self.loader = MyLoader()
    mock_ds = Mock()
    mock_ds_factory.get_ds_for_env.return_value = mock_ds
    self.loader.ds = mock_ds

def test_load(self):

    self.loader.ds.read_file.return_value = json.dumps(self.get_data())

    self.loader.load("test_s3_key") #####IN THIS LINE I AM GETTING ERROR AS MENTIONED BELOW##

@staticmethod
def get_data():
    return {"key1":"value1","key2":"value2"}

相关源位于此处：loaders-> myloader.py。myloader.py如下：

from common.ds_factory import DSFactory

class MyLoader:

   def __init__(self):

       self.ds = DSFactory.get_ds_for_env()


   def load(self, file_key):
       print(f"ds : {self.ds}")
       print(f"file read is : {self.ds.read_file(S3_BUCKET, file_key)}"}
       data_dict = json.loads(self.ds.read_file(S3_BUCKET, file_key))

但是在测试时，出现如下错误：

ds is :<MagicMock name='DSFactory.get_ds_for_env()' id='140634163567528'>
file read is :<MagicMock name='DSFactory.get_ds_for_env().read_file()' id='140635257259568'>

E               TypeError: the JSON object must be str, bytes or bytearray, not 'MagicMock'

我不明白为什么，即使在模拟read_file的返回值之后

self.loader.ds.read_file.return_value = json.dumps(self.get_data())

我正在获取MagickMock对象。我被困住了，不知道如何解决这个问题。

问题来源：stackoverflow