pytest-mypy-testing provides a pytest plugin to test that mypy produces a given output. As mypy can be told to display the type of an expression this allows us to check mypys type interference.
python -m pip install pytest-mypy-testing
The Python distribution package contains an entry point so that the plugin is automatically discovered by pytest. To disable the plugin when it is installed , you can use the pytest command line option -p no:mypy-testing.
A mypy test case is a top-level functions decorated with @pytest.mark.mypy_testing in a file named *.mypy-testing or in a pytest test module. pytest-mypy-testing follows the pytest logic in identifying test modules and respects the python_files config value.
Note that pytest-mypy-testing uses the Python ast module to parse candidate files and does not import any file, i.e., the decorator must be exactly named @pytest.mark.mypy_testing.
In a pytest test module file you may combine both regular pytest test functions and mypy test functions. A single function can be both.
Example: A simple mypy test case could look like this:
@pytest.mark.mypy_testing
def mypy_test_invalid_assignment() -> None:
foo = "abc"
foo = 123 # E: Incompatible types in assignment (expression has type "int", variable has type "str")
The plugin runs mypy for every file containing at least one mypy test case. The mypy output is then compared to special Python comments in the file:
# N: <msg> - we expect a mypy note message# W: <msg> - we expect a mypy warning message# E: <msg> - we expect a mypy error message# F: <msg> - we expect a mypy fatal error message# R: <msg> - we expect a mypy note message Revealed type is '<msg>'. This is useful to easily check reveal_type output:
@pytest.mark.mypy_testing
def mypy_use_reveal_type():
reveal_type(123) # N: Revealed type is 'Literal[123]?'
reveal_type(456) # R: Literal[456]?
The algorithm matching messages parses mypy error code both in the output generated by mypy and in the Python comments.
If both the mypy output and the Python comment contain an error code and a full message, then the messages and the error codes must match. The following test case expects that mypy writes out an assignment error code and a specific error message:
@pytest.mark.mypy_testing
def mypy_test_invalid_assignment() -> None:
foo = "abc"
foo = 123 # E: Incompatible types in assignment (expression has type "int", variable has type "str") [assignment]
If the Python comment does not contain an error code, then the error code written out by mypy (if any) is ignored. The following test case expects a specific error message from mypy, but ignores the error code produced by mypy:
@pytest.mark.mypy_testing
def mypy_test_invalid_assignment() -> None:
foo = "abc"
foo = 123 # E: Incompatible types in assignment (expression has type "int", variable has type "str")
If the Python comment specifies only an error code, then the message written out by mypy is ignored, i.e., the following test case checks that mypy reports an assignment error:
@pytest.mark.mypy_testing
def mypy_test_invalid_assignment() -> None:
foo = "abc"
foo = 123 # E: [assignment]
Skipping and Expected Failures
Mypy test case functions can be decorated with @pytest.mark.skip and @pytest.mark.xfail to mark them as to-be-skipped and as expected-to-fail, respectively. As with the @pytest.mark.mypy_testing mark, the names must match exactly as the decorators are extracted from the ast.
python -m pip install -U -r requirements.txt.pytest_collect_file() with usage of the file_path argument introduced in pytest 7 (#51, #52)PYTEST_VERSION_INFO - by @blueyed (#8)--check-untyped-defs to mypy (#11)python_files when identifying pytest test modules (#12)inv tox -e py-*) (#6)LICENSES directory (#6)RetroSearch is an open source project built by @garambo | Open a GitHub Issue
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