Lesson 14 — Automation

Unit Testing Frameworks

Unit testing frameworks provide the structure and tools — test runners, assertions, and reporting — needed to write and execute fast, focused tests of individual code units.

Anatomy of a Unit Test

Most unit tests follow the same simple structure: arrange the necessary setup, act by calling the function being tested, and assert that the result matches what was expected.

Python — A PyTest unit test 
def add(a, b):
    return a + b

def test_add_two_positive_numbers():
    # Arrange
    a, b = 2, 3
    # Act
    result = add(a, b)
    # Assert
    assert result == 5

Common Mistakes

  • Writing unit tests that depend on external systems (a real database or network call), blurring the line into integration testing and making tests slow and flaky.
  • Testing multiple unrelated behaviours in a single test function, making failures harder to diagnose.
  • Giving tests vague names like test1 instead of descriptive ones like test_add_rejects_negative_numbers.
  • Not testing edge cases and error conditions, only the simplest expected input.

Professional Tip

Name unit tests descriptively enough that a failure message alone tells you roughly what went wrong, e.g. test_divide_by_zero_raises_exception rather than test3.

Your Turn

Write three unit tests for a function that calculates a shopping cart's total: one for an empty cart, one for a single item, and one for multiple items.

Mini Quiz

What do the three steps 'Arrange, Act, Assert' describe in unit testing?