Using pytest#

pytest is a package that facilitates testing.

Creating the tests folder#

The first thing to do is to create a test folder in which all our tests will live.

src/
└── pydev_tutorial/
└── pydev_tutorial/
    └── swallow.py
tests/
├── __init__.py
└── test_swallow.py

Adding the test dependency group#

We need to tell the world that our package uses pytest, this will help IDE and continuous integration pipeline to run.

In your pyproject.toml, add the following lines:

[project.optional-dependencies]
# add dependencies used for testing here
test = ["pytest"]

This adds an optional dependency group, called test, which depends on pytest and pytest-cov. We will discuss the later in the coverage chapter.

Let's also add some pytest options:

[tool.pytest.ini_options]
minversion = "6.0"
testpaths = ["tests"]
filterwarnings = ["error"]

The most important here is to tell pytest where to find the tests themselves.

Install dependencies using the test group#

Rather than installing pytest directly, we can use the fact that it is now declared as a dependency group in our pyproject.toml:

pip install -e ".[test]"

This should install your package in editable mode, which is necessary to run the tests later, but also install all test dependencies.

Our first test#

In the test_swallow.py file, add the following test:

def test_my_module():
    pass

Yes, a minimal test is that simple... It is a function that starts with test_ and does something. Obviously pass is not very interesting here. But let's run it for the fun of it.