Testing is and will be essential when coding. To make our life easier, developers created many frameworks and helpers to quickly achieve high code coverage. One well know library for Python is Pytest, which we are going to use in this article.

Start a new project/folder using your favorite editor and create a requirements file for PIP, we are going to use test_requirements.txt. Add our only dependency:

pytest

Install our dependency with the following command (running from the folder where the test_requirements.txt is):

pip install -r test_requirements.txt

Now we can add our code file with the name basic_calculator.py:

def sum(numberOne: int, numberTwo: int):
    return numberOne + numberTwo

It doesn’t do anything fancy, just sums two number.

Now comes the test. Add a new file called test_basic_calculator.py:

import basic_calculator

class TestHandler:
    def test_sum_one(self):
        sum = basic_calculator.sum(2,3)
        assert sum == 5

    def test_sum_two(self):
        sum = basic_calculator.sum(66,55)
        assert sum == 121

We are done with coding, let’s run our test (give the following command from folder):

python -m pytest

The result should be something similar to this:

What happened here? We asked python to run the module called pytest in the working folder. Pytest then searches for filenames which start with “test_” and looks for classes starting with “Test” containing function names starting with “test”.

Narrowing down the test scope

We might want to run test only on one file, to do so we can specify it by name:

python -m pytest ./test_basic_calculator.py

There are further options as well

Run only one class in a file:

python -m pytest ./test_basic_calculator.py -k "Test_Handler"

or

python -m pytest ./test_basic_calculator.py::Test_Handler

If you only want to run one test in a class:

python -m pytest ./test_basic_calculator.py -k "Test_Handler and test_sum_one"

or

python -m pytest ./test_basic_calculator.py::Test_Handler::test_sum_one

Happy coding!