pytest-flake8-path 1.4.0

flake8_path fixture

A pytest fixture that wraps Pytest’s built-in tmp_path fixture (docs), to create a temporary directory, allow adding files, and running flake8. It acts like a pathlib.Path object, with one extra method.

If you’re using this to test a flake8 plugin, make sure flake8 is picking up your plugin during tests. Normally this is done with a setup.cfg entrypoint, which makes tox the easiest way to guarantee this is ready as it will install your project before running tests.

Flake8Result

Represents the parsed output of a flake8 run.

result = flake8_path.run_flake8()
expected = "./example.py:1:2: E221 multiple spaces before operator"
assert expected in result.out_lines

Basic

Using Path.write_text() (docs) we can create an example.py file with code. Then with flake8_path.run_flake8() we can run flake8 and check for an expected error:

def test_simple(flake8_path):
    (flake8_path / "example.py").write_text("x  = 1\n")

    result = flake8_path.run_flake8()

    assert result.out_lines == [
        "./example.py:1:2: E221 multiple spaces before operator"
    ]
    assert result.err_lines == []
    assert result.exit_code == 1

With dedent

The standard library’s textwrap.dedent() (docs) is useful for including multi-line files. Use a triple quoted multi-line string, with an initial backslash to prevent a blank first line:

def test_multi_line(flake8_path):
    (flake8_path / "example.py").write_text(
        dedent(
            """\
            x  = 1
            y  = 2
            """
        )
    )

    result = flake8_path.run_flake8()

    assert result.out_lines == [
        "./example.py:1:2: E221 multiple spaces before operator",
        "./example.py:2:2: E221 multiple spaces before operator",
    ]
    assert result.err_lines == []
    assert result.exit_code == 1

Configuring flake8

Write a setup.cfg file to configure flake8 before running it:

def test_with_setup_cfg(flake8_path):
    (flake8_path / "setup.cfg").write_text(
        dedent(
            """\
            [flake8]
            ignore = E221
            """
        )
    )
    (flake8_path / "example.py").write_text("x  = 1\n")

    result = flake8_path.run_flake8()

    assert result.out_lines == []
    assert result.err_lines == []
    assert result.exit_code == 0