how to write a test function for a function in python, WITHOUT class

Question

I want to test a function to see if it's working properly.

I found many answers such as how to write a unit testing function for my function? & unittest

But they all write the test functions under a certain class, while mine function isn't a member a any class.

for example I have this under readTool.py:

def extract_frame_dr(dr, frameID):
    return dr[0, frameID], dr[1, frameID]

How do I write a test_extract_frame_dr for it? I want to have the feature of Auto-discovery of test modules and functions: Run all the tests in readTool.py at once without calling them one by one in the main function.

Thanks

Answer 1

You may write very clear tests with functions using pytest. To do so,

1. Make your python modules to be importable in the test files (an example given in part 1)
2. Create test_x.py modules with test_y() functions, and run them with python -m pytest.

1. Folder structure & setup for writing tests

When writing code that you want to be tested, you need to ensure that your modules are importable by the test modules. Easiest way to do it would be to use folder structure like this:

.
│   setup.py
│   
├───mypackage
│       readTool.py
│       __init__.py
│
├───tests
│       test_readtool.py
│
└───venv

where setup.py is a file used to make your package installable. In this example, the file contents would be just

import setuptools

setuptools.setup(
    name='mypackage',
    packages=setuptools.find_packages(),
)

You also probably want to create a virtual environment (venv), activate it, and then install your package (mypackage) in an editable state with

pip install -e .

Then, install pytest

pip install pytest

(for more information on the usage of setup.py, see for example this answer)

2. Testing functions with functions

Write into tests/test_readtool.py:

from mypackage.readTool import extract_frame_dr


def test_extract_frame_dr():
    frame_id = 1963
    
    dr_who = {
        (0, frame_id): 'William Hartnell',
        (1, frame_id): 'Patrick Troughton',
    }

    extracted = extract_frame_dr(dr_who, frame_id)
    assert extracted[0] == 'William Hartnell'
    assert extracted[1] == 'Patrick Troughton'

and run the tests using

python -m pytest

(with just running pytest you may encounter into ModuleNotFoundErrors)

3. Auto-discovery of test modules and functions

This is part of pytest. Just

• Put your test files into the .\tests\ directory
• Name your test modules as test_x.py where as x a good convention would be to use the name of the module / package you are testing.
• Name your test functions as test_y(), where as y good convention is to write a short description for the test.