Testing frameworks

Each time we make changes to a code, we would like to test it. This can be tedious and that might prevent us from testing. We want to make testing as easy as version control is. A testing framework can help us.

py.test

The testing framework we will discuss today is a python library called pytest to automatically fetch all test files in the repository and execute them.

The pytest framework makes it easy to write small tests, yet scales to support complex functional testing for applications and libraries.

- pytest

In pytest, each test is a function whose name begins with the letters test. We can group tests together in files whose names also begin with the letters test. To execute our tests we run the command pytest. This automatically searches the current directory and its subdirectories for test files, and runs the tests they contain.

Consider the following method:

def inc(x):
    return x + 1

See the test_sample.py example:

# content of test_sample.py
def test_answer():
    assert inc(3) == 5

By simple executing pytest:

$ pytest
============================= test session starts =============================
collected 1 items

test_sample.py F

================================== FAILURES ===================================
_________________________________ test_answer _________________________________

    def test_answer():
>       assert inc(3) == 5
E       assert 4 == 5
E        +  where 4 = inc(3)

test_sample.py:5: AssertionError
========================== 1 failed in 0.04 seconds ===========================

Stepping back, the most important part of this lesson isn’t the details of the pytest library. It’s that your time is more valuable than the computer’s, so you should spend it doing the things computers can’t, like thinking of interesting test cases and what your code is actually supposed to do.