Writing Multiple Test Cases Together

This lesson covers how to run multiple test cases together, so you can efficiently verify a function's correctness. It's written for anyone searching "Python how to write test cases".

Testing a single function against multiple input patterns all at once is called unit testing. Preparing "normal values," "boundary values," and "special cases" ahead of time lets you catch bugs early. Managing test cases as a list of dictionaries also makes it easy to add more cases later.

The sample code gathers several input/expected-value pairs into a list called test_cases, then uses enumerate() to compare the result of add() against the expected value for each one. A variable called passed counts how many tests succeeded, and a final message summarizes "N out of N passed."

A common beginner mistake is testing only normal values and forgetting boundary cases like 0 or negative numbers, or other special cases. The idea of boundary-value testing is an important mindset for deliberately checking these "special situations" — many real bugs occur exactly at these boundary conditions.

In real development, it's standard practice to run tests like this automatically every time code changes, continuously verifying that existing functionality hasn't broken. A dedicated tool like Python's pytest makes automating this kind of testing even more efficient.