pytest.md

Pytest

The 2 most popular packages for testing are unittest and pytest, but others also exists. unittest is part of Python standard library. We currently use pytest as it allows compact test suites, special and simple class fixtures to facilitate testing.

The Pytest Testing article on the Real Python website gives a good description of the functionality of pytest and compares it to unittest. Most of the current examples in the documentation come from there, so see this original article and the official Pytest documentation for a complete description.

Run tests with:

pytest

Pytest features

• Runs test written for unittest framework.

• Files prefixed with test_ will be automatically run as tests.

• Check for markers in the pytest.ini config file. Otherwise markers could be mistyped and forgot when the number of tests grows.

  pytest --strict-markers

  Define markers in the pytest.ini file. (.toml file could be also used)

  [pytest]
  markers =
      slow: marks tests as slow (deselect with '-m "not slow"')
      network_access

  Run tests with a specific marker only:

  pytest -m network_access

  Deselect some tests:

  pytest -m "not slow"

  Pytest provides a few marks out of the box:

  • skip skips a test unconditionally.
  • skipif skips a test if the expression passed to it evaluates to True.
  • xfail indicates that a test is expected to fail, so if the test does fail, the overall suite can still result in a passing status.
  • parametrize creates multiple variants of a test with different values as arguments. You’ll learn more about this mark shortly.

• Show the n slowest tests:

  pytest --durations n

• Check code coverage

  pip install pytest-cov
  pytest --cov=mymodule tests/

• Fixtures provide a context for each test. They can be used for common and generic parts such as example input.

  @pytest.fixture
  def users():
      return [
          {"id": 1, "name": "foo"},
          {"id": 2, "name": "bar"}
      ]

  Use the previously defined fixture as a parameter.

  def test_users(users):
      assert users[1]["name"] == "bar"

• conftest.py file contains common fixtures and other generic overrides, such as disabling all network connection through the request.get command.