Tic Tac Toe kata

Rules

• The game is played on a grid that's 3 squares by 3 squares
• Players alternate placing X’s and O’s in empty squares
• X always plays first
• Players cannot play on a played square
• A Player wins when it has three squares in a row
  • Horizontally
  • Vertically
  • Diagonally
• If all nine squares are filled and neither player has won, the game is a draw

Follow TDD rules strictly

1. ✅ Write production code only to pass a failing unit test
2. ✅ Write only enough of a unit test to make it fail
3. ✅ Write only enough production code to make the failing test pass

First run

Implement Tic Tac Toe as best as you can using TDD.

Second run

Implement Tic Tac Toe strictly applying object calisthenics rules.

Object calisthenics

In order of importance (defined by Pedro)

• Wrap all primitives and strings
  • Wrap primitives in a type, specially if it has behaviour or it’s an important domain concept
• First class collections
  • Wrap collections in a type, specially if it has behaviour or it’s an important domain concept
• One dot per line
  • Do not write dog.Body.Tail.Wag() write dog.ExpressHappiness() - Law of Demeter
• No getters/setters/properties, no access to private data, none! - TELL DON’T ASK!
• No classes with more than two instance variables
• Only one level of indentation per method
• Don't use the ELSE keyword
• Don't abbreviate names
• Keep all entities small
  • 10 files per package/namespace
  • 50 lines per class
  • 5 lines per method
  • 2-3? arguments per method

Great habits

Considerations when writing a new test

• Tests should test one thing only.
• Create more specific tests to drive a more generic solution (triangulate).
• Give your tests meaningful names (behavior/goal-oriented) that reflect your business domain.
• See the test fail for the right reason.
• Ensure you have meaningful feedback from failing tests.
• Keep your tests and production code separate.
• Organize your unit tests to reflect your production code (similar project structure).
• Organize your test in arrange, act and assert blocks.
• Write the, or at least focus on the, assertion first and work backward.
• Write fast, isolated, repeatable and self-validating tests.

Considerations when making a failing test pass

• Write the simplest code to pass the test.
• Write any code that makes you get to the refactor phase quicker.
• Use Transformation Priority Premise.
• Consider using object calisthenics to drive design decisions.

Considerations after the test passes

• Use the Rule of Three to tackle duplication.
• Refactor design constantly.
• Apply object calisthenics to improve your design.

Resources

https://levelup.gitconnected.com/learn-these-9-rules-to-start-writing-clean-code-immediately-a7ee40fe1e1b https://williamdurand.fr/2013/06/03/object-calisthenics/