I wrote “TDD (Test-Driven Development) Overview with Python Example” to share practical, production-minded guidance on this topic.

How TDD Works

TDD is based on the Red-Green-Refactor cycle:

1. Write a test: write a test that fails because the functionality it tests doesn’t exist yet.
2. Make the test pass: write the minimum amount of code necessary to make the test pass.
3. Refactor: look for opportunities to improve the code and make it easier to maintain.

This cycle is repeated for each new piece of functionality. The result is a suite of tests that provide confidence in the code and make it easier to maintain and extend.

Here’s an example of how TDD works in Python:

Write a test

Start by writing a test that fails because the code it is testing hasn’t been written yet. This test should describe the desired behavior of the code that will be written.

def test_addition():
    assert add(2, 3) == 5

Run the test

Running the test should result in an error, because the add function hasn’t been defined yet.

NameError: name 'add' is not defined

Write Code

Now that the test is written, write just enough code to make the test pass.

def add(a, b):
    return a + b

Run the test (again)

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