pytest: Quick Start & Coverage Report

In this post, I am going to share how to use pytest.

Check https://docs.pytest.org/en/stable/getting-started.html for more detail.

What is pytest?

pytest is a testing framework for Python. https://docs.pytest.org/en/stable/

A similar technologies may include unittest, which is more like JUnit in my opinion.

Install

% pip install pytest
...
% pytest --version
pytest 6.2.1

Test

Let's start with a buggy code:

% cat test_sample.py 
def plus(x, y):
    return x * y

def test_answer():
    assert plus(2, 3) == 5

% pytest

==================================================================== test session starts =====================================================================
platform darwin -- Python 3.8.5, pytest-6.2.1, py-1.9.0, pluggy-0.13.1
rootdir: /Users/tomo/git/pytest
plugins: cov-2.10.1
collected 1 item                                                                                                                                             

test_sample.py F                                                                                                                                       [100%]

========================================================================== FAILURES ==========================================================================
________________________________________________________________________ test_answer _________________________________________________________________________

    def test_answer():
>       assert plus(2, 3) == 5
E       assert 6 == 5
E        +  where 6 = plus(2, 3)

test_sample.py:5: AssertionError
================================================================== short test summary info ===================================================================
FAILED test_sample.py::test_answer - assert 6 == 5
===================================================================== 1 failed in 0.06s ======================================================================

Fix it (replace * into +) and run again to see the success case.

Note "pytest will run all files of the form test_*.py or *_test.py in the current directory and its subdirectories" (https://docs.pytest.org/en/stable/getting-started.html).

Coverage

You can also use pytest-cov for coverage check.

% pip install pytest-cov

% pytest -v --cov=.

==================================================================== test session starts =====================================================================
platform darwin -- Python 3.8.5, pytest-6.2.1, py-1.9.0, pluggy-0.13.1 -- /Users/tomo/opt/anaconda3/bin/python
cachedir: .pytest_cache
rootdir: /Users/tomo/git/pytest
plugins: cov-2.10.1
collected 1 item                                                                                                                                             

test_sample.py::test_answer PASSED                                                                                                                     [100%]

---------- coverage: platform darwin, python 3.8.5-final-0 -----------
Name             Stmts   Miss  Cover
------------------------------------
test_sample.py       4      0   100%


===================================================================== 1 passed in 0.03s ======================================================================

To generate a HTML report,

% pytest -v --cov=. --cov-report=html

% open htmlcov/index.html