Test-Driven Development as if you meant it

An exercise for pushing Test-Driven Development to its limits.

Originally by Keith Braithwaite.

https://github.com/sf105/tdd-as-if-you-meant-it

Test-Driven Development isn't complicated

1. Add a little test
2. Run all the tests and watch the new one fail
3. Make a little change
4. Run all the tests and watch the new one pass
5. Refactor to remove duplication
6. Repeat until done

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But we observe many people doing "Pseudo-TDD"

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Let's turn it up to eleven

• This exercise turns up the TDD design constraints to full volume
• It's intended to show how unexpected designs can emerge from the process
• It's an exercise, it's not intended for everyday use
• It's suprisingly hard to get started

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TDD is about detailed feedback on design choices

• Thinking about solutions is not getting feedback
• Feedback comes from tests

Therefore:

Run tests early

• No, much earlier than that

Run tests often

• No, much more often than that

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In TDD, design thinking happens during refactoring

"Improving the design of existing code"

Existing code that you know works

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The exercise

Write code that, given a series of Tic-Tac-Toe^[1] moves, describes the state of the game.

1] Also known as "Noughts-and-crosses"

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Rules of the exercise

• Write one new test: The smallest you can think of that seems to point in the direction of a solution.
• Watch it fail
• Make the test pass by writing the least implementation code you can in the test method
• Refactor as required. To create new structure that's not test code, apply these steps very strictly.
  • methods:
    • (preferred) Extract Method to create a new method in the test class
    • (if necessary) Move code into an existing method
  • types:
    • create classes only to provide a destination for Move Method.
    • Populate classes by moving definitions from tests, not the other way round.
• The person not typing makes sure that these rules are being followed exactly.

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Version control

• check in on every green bar
• describe your current design thinking in the comment

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Discussion

• How did that feel?
• What is your code like?
• Any lessons learned?

Remember, this is just an exercise

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There's a sample solution the candidate-solution branch of this repository