Use Zombies in TDD

Contributed by: Maximiliano Contieri

Difficulty level: Intermediate

Test-driven development is a powerful development technique for building reliable software. You can incorporate it into your development workflow using the ZOMBIE approach. This method focuses on iterative progress, making sure your tests gradually increase in sophistication while maintaining control over the code’s logic and exploring testing paths in a methodic order.

The ZOMBIE methodology advises you to start with tests for Zero, One, and Many cases to verify your implementation. Using zombies in TDD helps you focus on building functionality incrementally while preventing premature complexity. The principle is simple: start with the simplest possible solution (even a hardcoded one), then evolve it into a more robust design over time.

The TDD ZOMBIE Cycle

To illustrate how the ZOMBIE cycle guides you in writing tests, we will build a classic Tic-tac-toe game in JavaScript using the ZOMBIE acronym:

Zero

Start by writing tests that handle cases when the input or game state is zero or empty.

One

Write tests that check how the system behaves when there is only one move or the smallest piece of data.

Many

Gradually introduce multiple moves or more complex scenarios to test.

Boundaries

Ensure that edge cases, like an already taken square, are handled.

Interfaces

Test public interfaces like methods and game APIs.

Exceptions

Finally, check how the game handles invalid inputs and exceptional ...