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 Coverage.py.

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", [("3+5", 8), ("2+4", 6), ("6*9", 42)])
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 monkeypatch 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!"