pytest plugin for testing mypy types, stubs, and plugins

Installation

pip install pytest-mypy-plugins

Usage

Running

Plugin, after installation, is automatically picked up by pytest therefore it is sufficient to just execute:

pytest

Paths

The PYTHONPATH and MYPYPATH environment variables, if set, are passed to mypy on invocation. This may be helpful if you are testing a local plugin and need to provide an import path to it.

Be aware that when mypy is run in a subprocess (the default) the test cases are run in temporary working directories where relative paths such as PYTHONPATH=./my_plugin do not reference the directory which you are running pytest from. If you encounter this, consider invoking pytest with --mypy-same-process or make your paths absolute, e.g. PYTHONPATH=$(pwd)/my_plugin pytest.

You can also specify PYTHONPATH, MYPYPATH, or any other environment variable in env: section of yml spec:

- case: mypy_path_from_env
  main: |
    from pair import Pair

    instance: Pair
    reveal_type(instance)  # N: Revealed type is 'pair.Pair'
  env:
    - MYPYPATH=./pytest_mypy_plugins/tests/fixtures

What is a test case?

In general each test case is just an element in an array written in a properly formatted YAML file. On top of that, each case must comply to following types:

Appendix to pseudo types used above:

class File:
    path: str
    content: Optional[str] = None
Parameter = Mapping[str, Any]

Implementation notes:

• main must be non-empty string that evaluates to valid Python code,
• content of each of extra files must evaluate to valid Python code,
• parametrized entries must all be the objects of the same type. It simply means that each entry must have exact same set of keys,
• skip - an expression set in skip is passed directly into eval. It is advised to take a peek and learn about how eval works.

Example

1. Inline type expectations

# typesafety/test_request.yml
- case: request_object_has_user_of_type_auth_user_model
  main: |
    from django.http.request import HttpRequest
    reveal_type(HttpRequest().user)  # N: Revealed type is 'myapp.models.MyUser'
    # check that other fields work ok
    reveal_type(HttpRequest().method)  # N: Revealed type is 'Union[builtins.str, None]'
  files:
    - path: myapp/__init__.py
    - path: myapp/models.py
      content: |
        from django.db import models
        class MyUser(models.Model):
            pass

2. @parametrized

- case: with_params
  parametrized:
    - val: 1
      rt: builtins.int
    - val: 1.0
      rt: builtins.float
  main: |
    reveal_type({[ val }})  # N: Revealed type is '{{ rt }}'

3. Longer type expectations

- case: with_out
  main: |
    reveal_type('str')
  out: |
    main:1: note: Revealed type is 'builtins.str'

Options

mypy-tests:
  --mypy-testing-base=MYPY_TESTING_BASE
                        Base directory for tests to use
  --mypy-ini-file=MYPY_INI_FILE
                        Which .ini file to use as a default config for tests
  --mypy-same-process
                        Now, to help with various issues in django-stubs, it runs every single test in the subprocess mypy call.
                        Some debuggers cannot attach to subprocess, so enable this flag to make mypy check happen in the same process.
                        (Could cause cache issues)

Further reading

• Testing mypy stubs, plugins, and types

License

MIT