Assertions

Result assertion may help us on testing functions. meiga provide us two functions: assert_success and access_failure.

How to assert

Following the example given on the getting started section:

With meiga 🧙Without meiga 😔

import pytest

from tests.unit.doc.example_without_meiga import (
    NoSuchKey,
    TypeMismatch,
    string_from_key,
)


@pytest.mark.unit
class TestExampleWithMeiga:
    dictionary = {"key1": "value", "key2": 2}

    def should_success(self):
        result = string_from_key(dictionary=self.dictionary, key="key1")
        result.assert_success(value_is_instance_of=str)

    def should_fail_when_key_does_not_exist(self):
        result = string_from_key(dictionary=self.dictionary, key="invalid_key")
        result.assert_failure(value_is_instance_of=NoSuchKey)

    def should_fail_when_type_mismatch(self):
        result = string_from_key(dictionary=self.dictionary, key="key2")
        result.assert_failure(value_is_instance_of=TypeMismatch)

import pytest

from tests.unit.doc.example_without_meiga import (
    NoSuchKey,
    TypeMismatch,
    string_from_key,
)


@pytest.mark.unit
class TestExampleWithoutMeiga:
    dictionary = {"key1": "value", "key2": 2}

    def should_return_a_str(self):
        value = string_from_key(dictionary=self.dictionary, key="key1")
        assert isinstance(value, str)

    def should_raises_non_such_key_exception(self):
        with pytest.raises(NoSuchKey):
            _ = string_from_key(dictionary=self.dictionary, key="invalid_key")

    def should_raises_type_mismatch_exception(self):
        with pytest.raises(TypeMismatch):
            value = string_from_key(dictionary=self.dictionary, key="key2")
            assert not isinstance(value, str)

Note

Check the following pytest-based test for more information: tests/unit/test_result_assertions.py

Warning

Before the version 1.7.0, the only way to assert results is with from meiga.assertions import assert_success, assert_failure.

import pytest
from meiga.assertions import assert_success, assert_failure
from meiga import Result


@pytest.mark.unit
class TestResultAssertion:
    def should_assert_a_success(self):
        result = Result(success=5)
        assert_success(result, value_is_instance_of=int)

For the shake of compatibility, this way of assertion is also supported. However, we strongly recommend to use Result class to perform auto assertion avoiding also import from meiga.assertions module.