mypy_test

Test mypy plugins, stubs, custom types.

Create a Python file, add comments to lines where you expect mypy to produce an error, run mypy_test, and it will check if actual errors are the same as you expect.

Features:

Flexible: supports every feature supported by mypy, does not enforce a project structure.
Fast: mypy gets run only once for all files at once. Also, no patching, no config generation.
Easy to learn: run mypy_test with the same arguments as you would run mypy, and it just works.
Lightweight: no dependencies except mypy.

python3 -m pip install mypy-test

Usage

Write a file you want to test, add comments to the lines you expect to fail:
```
a = 1
reveal_type(a)  # R: builtins.int
```
Run the tool:
```
python3 -m mypy_test example.py
```

Writing the comments

The comments have the following format: SEVERITY: MESSAGE.
Severity is a one-letter violation severity as reported by mypy.
- F for "fatal"
- E for "error"
- W for "warning"
- N for "note"
- R is a shorthand for N: Revealed type is "..."
Comment can be on the same line as the violation or on the line before.

Example:

var = 1.1
reveal_type(var)  # R: builtins.float

# E: Incompatible types in assignment (expression has type "str", variable has type "float")
var = ""

Tips:

The fastest way to know the severity and the message is to run mypy_test on the code and then copy-paste the resulting message.
Make separate functions for every test case, so it can have a nice description and a clean namespace.
Place all test files into one directory. For example, /types/ or /tests/types/.

Alternatives

pytest-mypy-plugins - pytest plugin, test cases described in a YAML file.
pytest-mypy-testing - pytest plugin, tests are described like pytest test cases (but they actually don't get run).

Dependencies of mypy-test (3).
Dependency	Optional
lxml	false
mypy	false
pytest	true

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mypy-test

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