pytest raises example

README.md

Simple scenario to demontrate how to assert for custom exception

============================================================================== test session starts ===============================================================================
platform darwin -- Python 3.7.10, pytest-6.1.1, py-1.11.0, pluggy-0.13.1 -- /python/.venv/bin/python3
cachedir: .pytest_cache
rootdir: /python, configfile: pytest.ini
plugins: Faker-13.3.3, anyio-3.5.0, mock-3.3.1, cov-2.10.1, icdiff-0.5
collected 5 items

test.py::test__get_status_ok[SUCCESS-True] PASSED                                                                                                                      [ 20%]
test.py::test__get_status_ok[FAILURE-False] PASSED                                                                                                                     [ 40%]
test.py::test__get_status_ok[PENDING-False] PASSED                                                                                                                     [ 60%]
test.py::test__get_status_invalid_payload PASSED                                                                                                                           [ 80%]
test.py::test__get_status_exception PASSED                                                                                                                             [100%]

=============================================================================== 5 passed in 0.12s ================================================================================

test.py

import pytest


class CustomException(Exception):
    MALFORMED_PAYLOAD_ERROR = "Malformed payload"
    INVALID_PAYLOAD_ERROR = "Invalid payload"
    _message: str = "Custom Exception"
    _error: str = ""

    def __init__(self, message: str = None, error: object = None):
        if message is not None:
            self._message = message

        if error is not None:
            self._error = error if isinstance(error, str) else repr(error)
        super().__init__(self._message)

    @property
    def message(self):
        return self._message

    @property
    def error(self):
        return self._error


class MyClass:
    STATUS_SUCCESS = "SUCCESS"
    STATUS_FAILURE = "FAILURE"
    STATUS_PENDING = "PENDING"

    def _get_status(self, payload: dict) -> bool:
        try:
            status = payload["body"]["status"]

            if status == self.STATUS_SUCCESS:
                return True
            elif status in (self.STATUS_FAILURE, self.STATUS_PENDING):
                return False
            else:
                raise CustomException(
                    message=CustomException.INVALID_PAYLOAD_ERROR,
                    error=status
                )

        except KeyError as exc:
            raise CustomException(
                message=CustomException.MALFORMED_PAYLOAD_ERROR,
                error=exc
            ) from exc


@pytest.mark.parametrize("payload_status, expected_result", [
    (MyClass.STATUS_SUCCESS, True),
    (MyClass.STATUS_FAILURE, False),
    (MyClass.STATUS_PENDING, False),
])
def test__get_status_ok(payload_status, expected_result):
    # Arrange
    payload = {"body": {"status": payload_status}}
    instance = MyClass()

    # Act
    status = instance._get_status(payload)  # pylint: disable=protected-access

    # Assert
    assert status == expected_result


def test__get_status_invalid_payload():
    # Arrange
    payload = {"body": {"status": "UNKNOWN"}}

    # Act
    with pytest.raises(CustomException) as exc_info:
        MyClass()._get_status(payload)  # pylint: disable=protected-access

    # Assert
    assert exc_info.value.message == CustomException.INVALID_PAYLOAD_ERROR
    assert exc_info.value.error == "UNKNOWN"


def test__get_status_exception():
    # Arrange
    payload = {"body": {}}
    instance = MyClass()

    # Act
    with pytest.raises(CustomException) as exc_info:
        instance._get_status(payload)  # pylint: disable=protected-access

    # Assert
    assert exc_info.value.message == CustomException.MALFORMED_PAYLOAD_ERROR
    assert exc_info.value.error == repr(KeyError("status"))