### Install pre-commit hooks

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/contributing.md

Install the pre-commit framework to automatically run style checks and formatting during commits.

```console
pre-commit install
```

--------------------------------

### Install pytest-mock

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/index.md

Install the pytest-mock package using pip.

```console
$ pip install pytest-mock
```

--------------------------------

### Basic Patching Example

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/index.md

Demonstrates how to use the mocker fixture to patch a module function and assert its call.

```python
import os

class UnixFS:

    @staticmethod
    def rm(filename):
        os.remove(filename)

def test_unix_fs(mocker):
    mocker.patch('os.remove')
    UnixFS.rm('file')
    os.remove.assert_called_once_with('file')
```

--------------------------------

### Install pytest-mock in editable mode with dev extras

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/contributing.md

Install the project in editable mode and include development dependencies. This is typically done after cloning the repository.

```console
pip install --editable .[dev]
```

--------------------------------

### Example of Improved Mock Call Assertion Error Reporting

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/configuration.md

This example demonstrates the enhanced pytest output for a failed mock call assertion (assert_called_once_with). It shows detailed introspection on differing call arguments.

```default
mocker = <pytest_mock.MockerFixture object at 0x0381E2D0>

    def test(mocker):
        m = mocker.Mock()
        m('fo')
>       m.assert_called_once_with('', bar=4)
E       AssertionError: Expected call: mock('', bar=4)
E       Actual call: mock('fo')
E
E       pytest introspection follows:
E
E       Args:
E       assert ('fo',) == ('',)
E         At index 0 diff: 'fo' != ''
E         Use -v to get the full diff
E       Kwargs:
E       assert {} == {'bar': 4}
E         Right contains more items:
E         {'bar': 4}
E         Use -v to get the full diff


test_foo.py:6: AssertionError
========================== 1 failed in 0.03 seconds ===========================
```

--------------------------------

### Type Annotating with MockerFixture

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/remarks.md

Use MockerFixture for static type checking in your tests. Ensure pytest-mock is installed and imported.

```python
from pytest_mock import MockerFixture

def test_foo(mocker: MockerFixture) -> None:
    ...
```

--------------------------------

### Patching with mocker

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/usage.md

Demonstrates basic usage of `mocker.patch` and `mocker.patch.object` for mocking functions and methods.

```python
def test_foo(mocker):
    # all valid calls
    mocker.patch('os.remove')
    mocker.patch.object(os, 'listdir', autospec=True)
    mocked_isfile = mocker.patch('os.path.isfile')
```

--------------------------------

### Using a stub for callbacks

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/usage.md

Shows how to use `mocker.stub` to create a mock object for testing callback functions.

```python
def test_stub(mocker):
    def foo(on_something):
        on_something('foo', 'bar')

    stub = mocker.stub(name='on_something_stub')

    foo(stub)
    stub.assert_called_once_with('foo', 'bar')
```

--------------------------------

### Unsupported Context Manager Usage

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/usage.md

Demonstrates the incorrect way to use mocker as a context manager. This pattern is discouraged and will trigger a warning.

```python
def test_context_manager(mocker):
    a = A()
    with mocker.patch.object(a, 'doIt', return_value=True, autospec=True):  # DO NOT DO THIS
        assert a.doIt() == True
```

--------------------------------

### Patching with contextlib.ExitStack

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/remarks.md

Shows an alternative to nested 'with' statements using 'contextlib.ExitStack' to manage multiple patch context managers. This improves indentation but can be more complex.

```python
import contextlib
import mock

def test_unix_fs():
    with contextlib.ExitStack() as stack:
        stack.enter_context(mock.patch('os.remove'))
        UnixFS.rm('file')
        os.remove.assert_called_once_with('file')

        stack.enter_context(mock.patch('os.listdir'))
        assert UnixFS.ls('dir') == expected
        # ...

        stack.enter_context(mock.patch('shutil.copy'))
        UnixFS.cp('src', 'dst')
        # ...

```

--------------------------------

### Patching with Decorators

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/remarks.md

Illustrates using 'mock.patch' as decorators for applying multiple patches. Note the disadvantages regarding parameter handling and dynamic unmocking.

```python
@mock.patch('os.remove')
@mock.patch('os.listdir')
@mock.patch('shutil.copy')
def test_unix_fs(mocked_copy, mocked_listdir, mocked_remove):
    UnixFS.rm('file')
    os.remove.assert_called_once_with('file')

    assert UnixFS.ls('dir') == expected
    # ...

    UnixFS.cp('src', 'dst')
    # ...

```

--------------------------------

### Run tests with tox for Python 3.8

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/contributing.md

Execute tests using tox for a specific Python environment (Python 3.8 in this case). This is a baseline check before submitting a Pull Request.

```console
tox -e py38
```

--------------------------------

### Enable Standalone Mock Package

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/configuration.md

Configure pytest to use the standalone 'mock' package from PyPI instead of the bundled unittest.mock. Add this to your pytest.ini file.

```ini
[pytest]
mock_use_standalone_module = true
```

--------------------------------

### Stopping a spy with mocker.stop

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/usage.md

Illustrates how to selectively stop a spy using `mocker.stop()` after it has been used.

```python
def test_with_unspy(mocker):
    class Foo:
        def bar(self):
            return 42

    spy = mocker.spy(Foo, "bar")
    foo = Foo()
    assert foo.bar() == 42
    assert spy.call_count == 1
    mocker.stop(spy)
    assert foo.bar() == 42
    assert spy.call_count == 1
```

--------------------------------

### Spying on a class method

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/usage.md

Shows how to use `mocker.spy` to track calls to a class method while still executing the original method.

```python
def test_spy_method(mocker):
    class Foo(object):
        def bar(self, v):
            return v * 2

    foo = Foo()
    spy = mocker.spy(foo, 'bar')
    assert foo.bar(21) == 42

    spy.assert_called_once_with(21)
    assert spy.spy_return == 42
```

--------------------------------

### Type Hinting with MockerFixture

Source: https://github.com/pytest-dev/pytest-mock/blob/main/CHANGELOG.rst

Use MockerFixture for type annotations in tests. This is the recommended approach for new code.

```python
from pytest_mock import MockerFixture

def test_foo(mocker: MockerFixture) -> None:
    ...
```

--------------------------------

### Nested Patching with Mock

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/remarks.md

Demonstrates excessive nesting of 'with' statements when using the standard 'mock' library for multiple patches. This can harm test readability.

```python
import mock

def test_unix_fs():
    with mock.patch('os.remove'):
        UnixFS.rm('file')
        os.remove.assert_called_once_with('file')

        with mock.patch('os.listdir'):
            assert UnixFS.ls('dir') == expected
            # ...

    with mock.patch('shutil.copy'):
        UnixFS.cp('src', 'dst')
        # ...

```

--------------------------------

### Spying on a module function

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/usage.md

Demonstrates spying on a function within a module to track its calls and return values.

```python
def test_spy_function(mocker):
    # mymodule declares `myfunction` which just returns 42
    import mymodule

    spy = mocker.spy(mymodule, "myfunction")
    assert mymodule.myfunction() == 42
    assert spy.call_count == 1
    assert spy.spy_return == 42
```

--------------------------------

### Disable Improved Mock Call Reporting

Source: https://github.com/pytest-dev/pytest-mock/blob/main/docs/configuration.md

Disable the feature that enhances pytest output for mock call assertion errors. Add this to your pytest.ini file if you encounter issues.

```ini
[pytest]
mock_traceback_monkeypatch = false
```

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