Skillshub common-tdd

Enforces Test-Driven Development (Red-Green-Refactor). Use when writing unit tests, implementing TDD, or improving test coverage for any feature. (triggers: **/*.test.ts, **/*.spec.ts, **/*_test.go, **/*Test.java, **/*_test.dart, **/*_spec.rb, tdd, unit test, write test, red green refactor, failing test, test coverage)

install

source · Clone the upstream repo

git clone https://github.com/ComeOnOliver/skillshub

Claude Code · Install into ~/.claude/skills/

T=$(mktemp -d) && git clone --depth=1 https://github.com/ComeOnOliver/skillshub "$T" && mkdir -p ~/.claude/skills && cp -r "$T/skills/HoangNguyen0403/agent-skills-standard/common-tdd" ~/.claude/skills/comeonoliver-skillshub-common-tdd && rm -rf "$T"

manifest: skills/HoangNguyen0403/agent-skills-standard/common-tdd/SKILL.md

source content

Test-Driven Development (TDD)

Priority: P1 (OPERATIONAL)

The Iron Law

NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST. Code written before the test must be deleted. Start over.

The TDD Cycle

RED: Write a minimal failing test. Verify failure (Expected error, not typo).
GREEN: Write simplest code to pass. Verify pass.
REFACTOR: Clean up code while staying green.

AAA Structure (Mandatory)

Every test must follow Arrange-Act-Assert:

Arrange: Set up inputs, stubs, mocks, and expected values.
Act: Call the single unit under test.
Assert: Verify output and side effects. One logical assertion per test. (See AAA Example for code structure).

Coverage Thresholds

Minimum: 80% (Statements, Functions, Lines), 75% (Branches).
Target: 90% (Statements, Functions, Lines), 85% (Branches).
Configure in test runner config (e.g.
```
jest.config.ts
```
,
```
vitest.config.ts
```
). Coverage below minimum is a build-gate failure.

Test Runner Commands

Language	Runner	Watch Mode	Coverage
TypeScript/JS	`jest` / `vitest`	`vitest --watch`	`vitest run --coverage`
Go	`go test`	`go test -v ./... -count=1`	`go test -cover ./...`
Java	JUnit 5 + Maven	`mvn test`	`mvn verify -P coverage`
Kotlin	JUnit 5 + Kotest	`./gradlew test`	`./gradlew jacocoTestReport`
Dart/Flutter	`flutter test`	`flutter test --watch`	`flutter test --coverage`

Core Principles

Watch it Fail: Prove the test works.
Minimalism: Don't add features/options beyond current test (YAGNI).
Real Over Mock: Prefer real dependencies unless slow/flaky.
One Reason to Fail: Test one behavior per test.
Descriptive Names: e.g.
```
should_returnError_when_emailIsInvalid
```
.

When to Use Mocks vs Real Dependencies

Database: Real DB (test container) or in-memory; mock as last resort.
HTTP/External APIs: Always mock.
Filesystem: Use temp dir; mock for unit isolation.
Time/Dates: Always mock/control.
Internal services: Real if fast (<200ms); mock if cross-network.

Verification Checklist

Every new function/method has a failing test first?
Failure message was expected?
Minimal code implemented passed?
AAA structure followed?
Coverage thresholds met?

Expert References

Anti-Patterns

No test-after: Writing tests post-implementation defeats TDD. Delete and restart.
No assertion-free tests: A test without an assert is not a test.
No testing implementation: Test behavior and contracts, not internal calls.