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I am trying to test my JsonWrite class and its write_json function that takes data from api and write it to a json file. This is my class.

import json
   
class JsonWriter:
    def write_json(self, weights, filename):
        try:
            json_data = json.dumps(weights, indent=4)
            
            with open(filename, 'w') as f:
                f.write(json_data)
                f.close()

        except Exception as e:
            return False, e

        return True, None

Should I break this write_json function to smaller units or is there a way of testing it? So far I have only mocked what it returns if everything is OK. But I think that isn't the right way of doing it. What am I missing here?

class JsonWrite(unittest.TestCase):

    @patch("argo_connectors.io.jsonwrite.JsonWriter.write_json")
    def test_read_file_data(self, mock_write_json):
        mock_write_json.return_value = True, None


if __name__ == '__main__':
    unittest.main()
dean89
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2 Answers2

0

You can try something like this:

  • Testing the dumping
  • Testing the writing

I hope this helps you...

import json
DEBUG = False


class JsonWriter:
    def dumps(self, weights):
        try:
            return True, json.dumps(weights, indent=4)
        except Exception as e:
            return False, e

    def write(self, json_data, filename):
        try:
            with open(filename, 'w') as f:
                f.write(json_data)
        except Exception as e:
            return False, e
        return True, None


def test_dumps(weigths, succeeded, data):
    success, result = json_writer.dumps(weigths)
    if DEBUG:
        print(success, "==", succeeded, "and", result, "==", data)
    assert success == succeeded and result == data


def test_write(json_data, filename, succeeded, exception):
    success, error = json_writer.write(json_data, filename)
    if DEBUG:
        print(success, "==", succeeded, "and", success, "==", exception)
    assert success == succeeded and error == exception


json_writer = JsonWriter()
test_dumps({}, True, "{}")
test_write("{}", "out.json", True, None)
print("All tests succeeded")
Nineteendo
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  • thank you for your help but I found [link](https://stackoverflow.com/questions/33184342/how-do-i-mock-an-open-write-without-getting-a-no-such-file-or-directory) to this solution that fits better IMO. Maybe I didn't explain correctly what I was needed. – dean89 Dec 28 '22 at 07:19
0

This is my solution for passing test and failing it:

mock_json = [
    {'id': 5414470, 'name': 'mike'},
    {'id': 5414472, 'name': 'tom'},
    {'id': 5414232, 'name': 'pete'},
]

mock_filename = "mock_file.json"


class JsonWriteTest(unittest.TestCase):
   def test_save_data_to_file(self):
        with patch('builtins.open', unittest.mock.mock_open()) as m:
          data_writer = JsonWriter(mock_json, 'mock_file.json')
          data_writer.write_json()

        m.assert_called_once_with('mock_file.json', 'w')
        handle = m()
        handle.write.assert_called_once_with('[\n    {\n        "id": 5414470,\n        "name": "mike"\n    },\n    {\n        "id": 5414472,\n        "name": "tom"\n    },\n    {\n        "id": 5414232,\n        "name": "pete"\n    }\n]')`

   def test_fail_jsonwrite(self):
      mock_jsondumps = Mock(name='json.dumps')
      mock_jsondumps.side_effect = Exception("Mocked error")

      with patch('json.dumps', mock_jsondumps):
         writer = JsonWriter({'mock_key': 'mock_value'}, mock_filename)
         result, error = writer.write_json()

         self.assertEqual(result, False)
         self.assertEqual(str(error), 'Mocked error')
dean89
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