TDD Workflow#

Write tests first, code second.

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1. The TDD Cycle#

text

🔴 RED → Write failing test
    ↓
🟢 GREEN → Write minimal code to pass
    ↓
🔵 REFACTOR → Improve code quality
    ↓
   Repeat...

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2. The Three Laws of TDD#

1. Write production code only to make a failing test pass
2. Write only enough test to demonstrate failure
3. Write only enough code to make the test pass

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3. RED Phase Principles#

What to Write#

FocusExampleBehavior"should add two numbers"Edge cases"should handle empty input"Error states"should throw for invalid data"

RED Phase Rules#

• Test must fail first
• Test name describes expected behavior
• One assertion per test (ideally)

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4. GREEN Phase Principles#

Minimum Code#

PrincipleMeaningYAGNIYou Aren't Gonna Need ItSimplest thingWrite the minimum to passNo optimizationJust make it work

GREEN Phase Rules#

• Don't write unneeded code
• Don't optimize yet
• Pass the test, nothing more

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5. REFACTOR Phase Principles#

What to Improve#

AreaActionDuplicationExtract common codeNamingMake intent clearStructureImprove organizationComplexitySimplify logic

REFACTOR Rules#

• All tests must stay green
• Small incremental changes
• Commit after each refactor

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6. AAA Pattern#

Every test follows:

StepPurposeArrangeSet up test dataActExecute code under testAssertVerify expected outcome

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7. When to Use TDD#

ScenarioTDD ValueNew featureHighBug fixHigh (write test first)Complex logicHighExploratoryLow (spike, then TDD)UI layoutLow

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8. Test Prioritization#

PriorityTest Type1Happy path2Error cases3Edge cases4Performance

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9. Anti-Patterns#

❌ Don't✅ DoSkip the RED phaseWatch test fail firstWrite tests afterWrite tests beforeOver-engineer initialKeep it simpleMultiple assertsOne behavior per testTest implementationTest behavior

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10. AI-Augmented TDD#

Multi-Agent Pattern#

AgentRoleAgent AWrite failing tests (RED)Agent BImplement to pass (GREEN)Agent COptimize (REFACTOR)

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Remember: The test is the specification. If you can't write a test, you don't understand the requirement.