Comparison with unittest.mock

Chainmock is built on top of Python's unittest.mock but provides a more intuitive and streamlined interface. Here are some key advantages of using Chainmock:

• Automatic teardown: Chainmock handles mock cleanup automatically at the end of each test.
• Lazy evaluation: Assertions are evaluated during teardown, not immediately when called.
• Method chaining: Multiple assertions can be chained together in a single line.
• Less boilerplate: More concise syntax for common mocking patterns.

Chainmock also provides some additional features not available in unittest.mock, such as:

• Partial argument matching.
• More granular call count assertions (e.g., call_count_at_least, call_count_at_most).
• Spying without mocking which is not directly supported by unittest.mock.

Let's look at some practical examples comparing unittest.mock and Chainmock approaches.

Basic mocking and assertions

Mocking a method return value

With unittest:

teapot = Teapot()
with mock.patch.object(teapot, 'add_tea') as mocked:
    mocked.return_value = 'mocked'
    assert teapot.add_tea('green') == 'mocked'
    mocked.assert_called_once_with('green')

With Chainmock:

teapot = Teapot()
mocker(teapot).mock('add_tea').return_value('mocked').called_once_with('green')
assert teapot.add_tea('green') == 'mocked'

Side effects and exceptions

Raising exceptions

With unittest:

teapot = Teapot()
with mock.patch.object(teapot, 'brew') as mocked:
    mocked.side_effect = ValueError("No tea!")
    try:
        teapot.brew()
    except ValueError as e:
        assert str(e) == "No tea!"
    mocked.assert_called_once()

With Chainmock:

teapot = Teapot()
mocker(teapot).mock('brew').side_effect(ValueError("No tea!")).called_once()
try:
    teapot.brew()
except ValueError as e:
    assert str(e) == "No tea!"

Sequential return values

With unittest:

teapot = Teapot()
with mock.patch.object(teapot, 'fill') as mock_fill:
    mock_fill.side_effect = ['full', 'overfull', 'spilling']
    assert teapot.fill() == 'full'
    assert teapot.fill() == 'overfull'
    assert teapot.fill() == 'spilling'
    assert mock_fill.call_count == 3

With Chainmock:

teapot = Teapot()
mocker(teapot).mock("fill").side_effect(
    ["full", "overfull", "spilling"]
).call_count(3)
assert teapot.fill() == 'full'
assert teapot.fill() == 'overfull'
assert teapot.fill() == 'spilling'

Stubs

Stubbing attributes

With unittest:

stub = mock.Mock()
stub.attribute = 'value'
stub.other_attribute = 'other_value'
assert stub.attribute == 'value'
assert stub.other_attribute == 'other_value'

With Chainmock:

stub = mocker(attribute='value', other_attribute='other_value')
assert stub.attribute == 'value'
assert stub.other_attribute == 'other_value'

Stubbing methods

With unittest:

stub = mock.Mock()
stub.method.return_value = 'mocked'
assert stub.method() == 'mocked'

With Chainmock:

stub = mocker(method=lambda: 'mocked')
assert stub.method() == 'mocked'