Whitebox testing an error raising custom validation rule is not supported

[weshouman]

Brief

Adding errors in a custom validator rule prevents direct trigger of this rule

Current Behaviour

Creating a validation rule like

    def _validate_is_duration(self, is_duration, field, value):
        """ 
        Test if a field's value is a valid duration format 
        The rule's arguments are validated against this schema:
            {'type': 'boolean'}
        """
        if is_duration:
            duration_pattern = r'^(\d+-\d+ weeks|\d+ weeks|\d+-\d+ months|\d+ months|\d+-\d+ years|\d+ years)$'
            if not re.match(duration_pattern, value):
                self._error(field, f"Duration '{value}' is invalid")

and trying to trigger it using

    def setUp(self):
        self.validator = MyValidator({
            'duration': {'type': 'string', 'is_duration': True}
        })

    def test_duration_invalid(self):
        self.validator._validate_is_duration(True, 'duration', '6 decades')
        ...

Would give the error

  File "/path/to/project/venv/lib/python3.11/site-packages/cerberus/validator.py", line 280, in _error
    self._error(args[0], errors.CUSTOM, args[1])
  File "/path/to/project/venv/lib/python3.11/site-packages/cerberus/validator.py", line 308, in _error
    value = self.document.get(field)
            ^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'get'

Expected Behaviour

Either:

• Validation occurs and error is captured instead of accessing get on None
• A not-initialized validator exception be raised

Workarounds

The following workarounds would work

Content Initialization

Initializing the validator.document to a dictionary would suppress the exception (with a wrong value set)

    def test_duration_invalid(self):
        self.validator.document = {}
        self.validator._validate_is_duration(True, 'duration', '6 decades')
        print(self.validator.recent_error)

Validating Whole Content

In more complete scenarios that may unnecessarily test other aspects''

    def test_duration_invalid(self):
        self.validator.validate({"duration": "6 decades"})
        print(self.validator.errors)
        print(self.validator.recent_error)