red-green-refactor

name: red-green-refactor description: TDD Red-Green-Refactor 사이클 가이드. 테스트 주도 개발 시 실패하는 테스트 작성(Red), 최소한의 코드로 통과(Green), 리팩토링(Refactor) 순서를 따를 때 사용. Kotest DescribeSpec 기반 Kotlin/JVM 프로젝트에서 TDD 실천 시 활용.

TDD Red-Green-Refactor Cycle

Red Phase: Write Failing Test

1. Express intended behavior as test first
2. Test only one behavior at a time
3. Must verify failure by running test (compilation errors count as failures)

// Kotest DescribeSpec example
class CalculatorTest : DescribeSpec({
    describe("Calculator") {
        it("두 숫자를 더한다") {
            val calculator = Calculator()
            calculator.add(2, 3) shouldBe 5
        }
    }
})

Verify failure message matches intent. Unexpected failure reasons indicate test issues.

Green Phase: Make Test Pass

1. Write minimal code to pass the test
2. Hardcoding, duplication, messy code allowed
3. Goal is only green bar

class Calculator {
    fun add(a: Int, b: Int): Int = 5  // Hardcoding OK
}

"Working code" first, "clean code" next.

Refactor Phase: Improve Code

1. Keep tests passing while improving
2. Remove duplication, improve naming, apply patterns
3. Must re-run tests after refactoring
4. No new features - structural improvements only

class Calculator {
    fun add(a: Int, b: Int): Int = a + b  // Generalize
}

Cycle Rules

• No production code without test
• No production code changes without failing test
• Commit after passing tests (keep commits small)
• No new features during refactoring
• Minimize test changes during refactoring

Checklist

Red

• Test verifies single behavior?
• Verified failure by running test?
• Failure message as intended?

Green

• Passed with simplest approach?
• Test is green?

Refactor

• Tests still green?
• Duplication removed?
• Names reveal intent?
• No new features added?