CODEWITHSUNDEEP
pythonpython-3.xpython-mock
yesh
yesh

Reputation: 2070

Mocking file open and throwing exception

I am new to python testing. I am using pytest and started learning about mocks and patches. I am trying to write a test case for one of my methods.

helper.py

def validate_json_specifications(path_to_data_folder, json_file_path, json_data) -> None:

    """ Validates the json data with a schema file.
    :param path_to_data_folder: Path to the root folder where all the JSON & schema files are located.
    :param json_file_path: Path to the json file
    :param json_data: Contents of the json file
    :return: None
    """

    schema_file_path = os.path.join(path_to_data_folder, "schema", os.path.basename(json_file_path))
    resolver = RefResolver('file://' + schema_file_path, None)
    with open(schema_file_path) as schema_data:
        try:
            Draft4Validator(json.load(schema_data), resolver=resolver).validate(json_data)
        except ValidationError as e:
            print('ValidationError: Failed to validate {}: {}'.format(os.path.basename(json_file_path), str(e)))
            exit()

Things I want to test are:

  1. Is the Draft4Validator class instantiated and the validate method is invoked with the json_data?
  2. Is ValidationError thrown and exit is called?

Here is my attempt at writing a test case so far. I decided to patch open method & Draft4Validator class.

@patch('builtins.open', mock_open(read_data={}))
@patch('myproject.common.helper.jsonschema', Draft4Validator())
def test_validate_json_specifications(mock_file_open, draft_4_validator_mock):
    validate_json_specifications('foo_path_to_data', 'foo_json_file_path', {})
    mock_file_open.assert_called_with('foo_path_to_data/schema/foo_json_file_path')
    draft_4_validator_mock.assert_called()

I wanted to pass some fake data and paths to my method instead of trying to pass real data. I got this error message

UPDATE:

    @patch('myproject.common.helper.jsonschema', Draft4Validator())
E   TypeError: __init__() missing 1 required positional argument: 'schema'

How do I go about creating patches for 2 methods specially Draft4Validator and how do I simulate ValidationError exception?

Upvotes: 1

Views: 2437

Answers (1)

Enrique Saez
Enrique Saez

Reputation: 2700

You were patching the Draft4Validator wrong. Basically what you were doing is creating a new Draft4Validator object without the required arguments and assigning it to the myproject.common.helper.jsonschema call everytime (had you created it with the required arguments).

Read more about it here: https://docs.python.org/3/library/unittest.mock-examples.html#patch-decorators

For checking assertions about expected exceptions check: http://doc.pytest.org/en/latest/assert.html#assertions-about-expected-exceptions

I guess by your question and requirements that you want something along the lines of this:

@patch('sys.exit')
@patch('myproject.common.helper.jsonschema.Draft4Validator')
@patch('builtins.open')
def test_validate_json_specifications(mock_file_open, draft_4_validator_mock, exit_mock):
    with pytest.raises(ValidationError):
        mock_file_open.return_value = {}
        draft_4_validator_mock = Mock()
        draft_4_validator_mock.side_effect = ValidationError

        validate_json_specifications('foo_path_to_data', 'foo_json_file_path', {}) 

        assert draft_4_validator_mock.call_count == 1
        assert draft_4_validator_mock.validate.assert_called_with({})        
        assert exit_mock.call_count == 1

Upvotes: 2

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