typest

An experimental framework to test your library against type checkers, allowing to formulate type expectations and expected typechecker errors. Its purpose is the same as the one of pytest-mypy-plugins. While pytest-mypy-plugins requires .yaml files for specifying the tests, typest test cases are python files, expectations are formulated in comments:

from mylibrary import some_function

result = some_function()

reveal_type(result)  # expect-type: int

Besides expressing type expectations, you can also specify to expect an error from the typechecker:

string: str = "not a number"
number: int = string  # expect-error

You can also specify to expect a mismatch error, i.e. an error where an assigned type is mismatching the actual type:

string: str = "not a number"
number: int = string  # expect-mismatch: int <> str

Suppported Typecheckers

• mypy
• pyright

Installation

typest is available at pypi. You can install it through pip:

pip install typest

Use

python -m typest [PATH] [TYPECHECKERS]

If PATH is a directory, all python files under that directory (including subdirectories) are going to be checked. If PATH points to a file, it has to be a python file.

TYPECHECKERS is an optional argument, a comma separated list of names of typecheckers you want to run your tests against. Currently, mypy and pyright are suppported.

Development

You can add more typecheckers by subclassing typest.typecheckers.base.TypeChecker and importing your new class in typest/typecheckers/__init__.py.