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Canon TDD Workflow

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Reference for Kent Beck's test-driven development process.

The Five Steps

Step Name Focus Color
1 List Behavioral variants -
2 Test Write one test Red
3 Pass Make it work Green
4 Refactor Improve design Blue
5 Repeat Next from list -

Step Details

Step 1: List

Purpose: Identify all expected behavioral variants and edge cases.

Activities:

  • Analyze requirements
  • Identify success cases
  • Identify failure cases
  • Consider edge cases
  • Document as test list

Output: Written list of tests to implement.

Step 2: Test (Red)

Purpose: Write one failing test from the list.

Focus: Interface design - how behavior is invoked from caller perspective.

Activities:

  • Setup test context
  • Invoke the behavior
  • Assert expected outcome
  • Run test - should fail

Output: One failing test.

Step 3: Pass (Green)

Purpose: Make the test pass with minimum code.

Focus: Implementation design - internal mechanics.

Rules:

  • Write only enough code to pass
  • No shortcuts (hardcoding values)
  • No additional features

Output: Passing test.

Step 4: Refactor (Blue)

Purpose: Improve code design without changing behavior.

Activities:

  • Extract methods
  • Rename for clarity
  • Remove duplication
  • Improve structure

Constraint: All tests must still pass.

Step 5: Repeat

Purpose: Continue until test list is empty.

Note: New tests discovered during implementation get added to the list.

Red-Green-Refactor Cycle

Red → Green → Refactor → Red → Green → Refactor → ...
Phase Activity Tests
Red Write failing test 1 failing
Green Make test pass All passing
Refactor Improve design All passing

Key Principles

Principle Description
Red = Interface Focus on how behavior is called
Green = Implementation Focus on making it work
Small steps One test at a time
Test list Plan before coding
Emergent design Design improves through refactoring

Example Test List

For feature init-project:

Test List:
- [ ] Create config in empty directory (success)
- [ ] Create config with custom path (success)
- [ ] Create config when file exists (error)
- [ ] Create config in read-only directory (error)
- [ ] Create config with invalid path (error)

Anti-Patterns

Anti-Pattern Problem Fix
Skipping Red Don't know test works Always see test fail first
Gold-plating Over-engineering Only pass current test
Skipping Refactor Technical debt Refactor after every Green
Big steps Hard to debug One behavior per test

Reference

Based on Canon TDD by Kent Beck.

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