pytest

Usage⚑

Invoke with python -m pytest so that the current directory is included to the python path.

Execute just one test or test class⚑

pytest test_server.py::TestClass::test_method

or

pytest test_server.py::TestClass

Coverage⚑

To see which parts of your code are executed when running the tests, you can use (https://coverage.readthedocs.io/).

You can install it with pip install coverage.

The basic usage is:

coverage run --source={{path}} -m pytest
coverage report -m # view report summary in the command-line
coverage html # generate detailed report in htmlcov/index.html

100% coverage doesn't mean that all the code is tested, it means that all the code was executed at least once while running the tests. 100% coverage is necessary but not sufficient for ensuring that all code is tested.

Reference⚑

Parametrization⚑

To run the same test several times with different variables use @pytest.mark.parametrize().

import pytest


@pytest.mark.parametrize("test_input,expected", )
def test_eval(test_input, expected):
    assert eval(test_input) == expected

Mocking⚑

monkeypatch⚑

Sometimes tests need to invoke functionality which depends on global settings or which invokes code which cannot be easily tested such as network access. The (https://docs.pytest.org/en/latest/how-to/monkeypatch.html) fixture helps you to safely set/delete an attribute, dictionary item or environment variable, or to modify sys.path for importing.

You need to add monkeypatch as an argument to the test functions.

Environment variables⚑

monkeypatch.setenv(name, value, prepend=None)

Fixtures⚑

To run a custom function for every test in a class do:

class TestClass:
    @pytest.fixture(autouse=True)
    def setup(self):
        self.variable = 42

    def test_something(self):
        ...

capfd⚑

Capture stdout/stderr output.

Example:

def test_foo(capfd):
    foo()  # Writes "Hello World!" to stdout
    out, err = capfd.readouterr()
    assert out == "Hello World!"