Test Driven Development

Execute

→ False-positive entry on a native-direct-skill host? → Exit immediately unless the user explicitly asked for TDD or the conversation already contains TDD Route: strict. In off mode, do not start RED / GREEN / REFACTOR from generic bugfix, contract, shared-module, or risky-code wording alone. Hand control back to using-aegis, systematic-debugging, writing-plans, or the fast path with verification. → Implementing a feature or bugfix under TDD Route strict? → No production code without a failing test first. Gate: medium/high complexity? → route to brainstorming or writing-plans first. Mode: auto chooses strict/light/skipped by risk; off disables automatic TDD, not completion verification. Change Necessity: before strict RED/GREEN enters production edits, confirm the slice really needs a code change. Cycle: RED (write test → watch it fail) → GREEN (minimal code → watch it pass) → REFACTOR (clean up → keep green) Regression: shared module → related tests. contract change → producer + consumer. core logic → old + new tests. Ripple signal hit → cover producer+consumer or real user path before claiming green. GREEN proves the currently expressed behavior slice only. GREEN does not by itself prove parent-task acceptance, business-value completion, or final completion. → Done when: chosen TDD Route is recorded, strict-route tests pass, TDD preflight gate passed when applicable, pre-edit complexity risk was checked for non-trivial source edits, and verification-before-completion has fresh evidence.

Test-Driven Development (TDD)

Overview

Write the test first. Watch it fail. Write minimal code to pass.

If you didn't watch the test fail, you don't know if it tests the right thing.

TDD Mode has two values: auto and off. auto lets Aegis choose a TDD Route; off disables automatic TDD routing but never disables verification-before-completion.

On native-direct-skill hosts, automatic entry must stay anchored to literal conversation markers such as TDD Route: strict, strict TDD, test-first, or RED / GREEN / REFACTOR, not generic risky-implementation wording.

When to Use

Only enter this skill after one of these explicit entry signals exists:

• the user explicitly asks for strict TDD, test-first development, or RED / GREEN / REFACTOR
• the current conversation already contains TDD Route: strict from another Aegis workflow

Typical strict-route shapes once entry is already justified: new features, bug fixes, refactoring, behavior or logic changes, interface/data contract changes, cross-module or shared-module changes, and core logic refactors.

Exceptions (ask your human partner): throwaway prototypes, generated code, config files, pure docs cleanup, read-only diagnosis, comment-only changes.

TDD Mode and Route

Before source edits, decide:

TDD Route:
- Mode: auto | off
- Decision: strict | light | skipped
- Reason:
- Verification:

In auto, use strict for behavior, bugfix, contract, shared/core, producer / consumer, persistence, permission, migration, or meaningful regression risk. Use light for tiny low-risk edits with an obvious readback or command check. Use skipped for read-only, docs-only, generated, throwaway, comment-only, or environment-bound work where TDD does not fit.

In off, do not automatically require TDD. Explicit user/project TDD requests still apply, and risky work may still justify recommending strict TDD. verification-before-completion still applies before any completion claim. If this skill was loaded anyway without an explicit TDD request or a visible TDD Route: strict marker, exit instead of improvising an automatic strict route from risk words alone.

Preflight Gate

TDD is the implementation discipline for an approved behavior or atomic task. It is not a substitute for task routing, product clarification, or planning.

Before writing tests or production code, stop and route to brainstorming or writing-plans if the current request has any medium- or high-complexity signal:

• multiple files, modules, pages, screens, services, or owners
• user-visible flows such as navigation, onboarding, checkout, lifecycle, or

recovery paths

• state transitions, routing rules, API or data contracts, compatibility

boundaries, migrations, permissions, or persistence

• more than one acceptance path or manual/visual verification requirement
• unclear product behavior, competing constraints, or long-running execution

For these tasks, require a baseline read-set, plan, and atomic tasks before TDD. High-complexity or ambiguous tasks also need a spec/design review before planning. Only proceed directly with TDD for low-complexity work whose intent, owner, compatibility boundary, verification path, and slice goal / success evidence are already clear.

Change Necessity

Before strict RED/GREEN enters production code edits, make the code-change decision visible. This is the "should code change at all?" check; it is not a new artifact and does not belong in the using-aegis hot path.

Change Necessity:
- User-visible need:
- No-change / non-code option:
- Why code change is necessary:
- Minimum change boundary:
- Decision: no-change | docs/config-only | code-change | needs-clarification

If the decision is no-change, do not write tests or production code for a non-change. If the decision is docs/config-only, route to that narrower surface and verify it. If the decision is needs-clarification, pause before RED/GREEN. If the decision is code-change, carry the minimum boundary into TDD Route, RED, and regression scope.

Complexity Budget

Before strict TDD on non-trivial work, record the planned complexity budget so RED/GREEN does not silently normalize a wrong or overloaded owner.

Complexity Budget:
- Artifact class:
- Current pressure:
- Projected post-change pressure:
- Planned governance:

Use using-aegis/references/complexity-governance.md for shared artifact classes, pressure signals, and the meaning of planned governance.

Pre-Edit Complexity Check

Before production code edits, check whether the intended source edit would add logic to an overloaded or wrong owner. Tiny edits can keep this to one line.

Use using-aegis/references/complexity-governance.md for shared pressure signals and the meaning of over-budget.

Pre-Edit Complexity Check:
- Target edit file:
- Existing pressure signal:
- Owner fit:
- Safer edit boundary:
- Decision: edit-in-place | extract helper | add owner file | split task | pause for plan update

If the decision is pause for plan update, stop TDD and return to writing-plans or brainstorming with the evidence.

If the predicted result is that this slice would push a maintained artifact over budget and the slice does not also govern that overrun, do not continue with RED/GREEN as if the task were safely scoped. Pause and update the plan.

When a medium- or high-complexity task needs project records, use configured Aegis workspace support lazily. Prefer the installed Aegis workspace helper (python init --root ) when it is available. If the task needs a process trail under work/, prefer python new-work --root ... so the intent, checkpoint, drift, and evidence paths are indexed and structurally checkable:

docs/aegis/
  README.md
  INDEX.md
  BASELINE-GOVERNANCE.md
  adr/
  baseline/
  specs/
  plans/
  work/YYYY-MM-DD-/
    10-intent.md
    20-checkpoint.md
    90-evidence.md
    99-reflection.md

Do not promote reusable project facts, decisions, specs, or plans into those directories unless the workflow needs them and no existing project authority already owns them.

Red-Green-Refactor

RED - Write Failing Test

State: input | output | boundary | acceptance criteria. Check existing test coverage first. Write one minimal test showing what should happen. A minimal test anchors the next behavior slice; it does not by itself define whole-task completeness unless the parent acceptance is already fully pinned.

test('retries failed operations 3 times', async () => {
  let attempts = 0;
  const operation = () => {
    attempts++;
    if (attempts 

```typescript
test('retry works', async () => {
  const mock = jest.fn()
    .mockRejectedValueOnce(new Error())
    .mockRejectedValueOnce(new Error())
    .mockResolvedValueOnce('success');
  await retryOperation(mock);
  expect(mock).toHaveBeenCalledTimes(3);
});

Vague name, tests mock not code

Requirements:

• One behavior
• Clear name
• Real code (no mocks unless unavoidable)
• If a new feature changes user-observable behavior, prefer one minimal

end-to-end or integration test for the main path before narrower unit tests

• For user-visible work, cover the main journey and the highest-risk experience

or operational floor before treating unit tests as sufficient

• Add unit tests for core rules, boundary conditions, and error branches

Verify RED - Watch It Fail

MANDATORY. Never skip.

npm test path/to/test.test.ts

Confirm:

• Test fails (not errors)
• Failure message is expected
• Fails because feature missing (not typos)

Test passes? You're testing existing behavior. Fix test.

Test errors? Fix error, re-run until it fails correctly.

GREEN - Minimal Code

Write simplest code to pass the test.

async function retryOperation(fn: () => Promise): Promise {
  for (let i = 0; i 

```typescript
async function retryOperation(
  fn: () => Promise,
  options?: {
    maxRetries?: number;
    backoff?: 'linear' | 'exponential';
    onRetry?: (attempt: number) => void;
  }
): Promise {
  // YAGNI
}

Over-engineered

Don't add features, refactor other code, or "improve" beyond the test.

Fix the real owner of the behavior. Do not add a new fallback, adapter, or branch unless the debugging or design workflow identifies why it is necessary and what old path retires.

Verify GREEN - Watch It Pass

MANDATORY.

npm test path/to/test.test.ts

Confirm:

• Test passes
• Other tests still pass
• Output pristine (no errors, warnings)

Test fails? Fix code, not test.

Other tests fail? Fix now.

REFACTOR - Clean Up

After green only:

• Remove duplication
• Improve names
• Extract helpers

Keep tests green. Don't add behavior.

Repeat

Next failing test for next feature.

Regression Scope

At minimum, run the target test you just changed or added. Broaden regression based on impact:

• Shared module change -> related module tests
• Interface or data contract change -> producer and consumer tests
• Cross-module behavior change -> integration or end-to-end path
• Core logic refactor -> old behavior regression tests plus new behavior tests
• Ripple Signal Triage fired -> producer+consumer or real user path that proves

the downstream effect remains bounded

If the current environment cannot run automated tests, state the blocker and provide reproducible manual verification steps.

Good Tests

| Quality | Good | Bad | |---------|------|-----| | Minimal | One thing. "and" in name? Split it. | test('validates email and domain and whitespace') | | Clear | Name describes behavior | test('test1') | | Shows intent | Demonstrates desired API | Obscures what code should do |

Red Flags - STOP and Start Over

• Code before test
• Test after implementation
• Test passes immediately
• Can't explain why test failed
• Tests added "later"
• Rationalizing "just this once"
• "I already manually tested it"
• "Tests after achieve the same purpose"
• "It's about spirit not ritual"
• "Keep as reference" or "adapt existing code"
• "Already spent X hours, deleting is wasteful"
• "TDD is dogmatic, I'm being pragmatic"
• "This is different because..."

All of these mean: Delete code. Start over with TDD.

Example: Bug Fix

Bug: Empty email accepted

RED

test('rejects empty email', async () => {
  const result = await submitForm({ email: '' });
  expect(result.error).toBe('Email required');
});

Verify RED

$ npm test
FAIL: expected 'Email required', got undefined

GREEN

function submitForm(data: FormData) {
  if (!data.email?.trim()) {
    return { error: 'Email required' };
  }
  // ...
}

Verify GREEN

$ npm test
PASS

REFACTOR Extract validation for multiple fields if needed.

Verification Checklist

• [ ] Defined input, output, boundaries, compatibility, acceptance criteria
• [ ] Every new function/method has a test that failed first
• [ ] All tests pass, output pristine
• [ ] Regression: shared/contract/core changes ran related tests
• [ ] Ripple signal hit: downstream or real user path covered
• [ ] If automation blocked → blocker + manual steps documented
• [ ] GREEN treated as local behavior proof only, not final completion
• [ ] If TaskIntentDraft, parent plan/spec, or Slice Card exists, covered and uncovered scope are explicit before any done claim

Can't check all boxes? Start over.

Exploration and Emergency Exceptions

Exploratory spikes are allowed only as throwaway learning. When the spike ends, convert confirmed behavior into tests before formal implementation.

Emergency hotfixes may prioritize the smallest safe repair when delay is more dangerous than incomplete TDD. Record the reason, keep the change narrow, and add the missing regression test in the same slice or the next nearest slice.

When Stuck

Don't know how to test → write wished-for API first. Test too complicated → simplify design. Must mock everything → reduce coupling.

Debugging Integration

Bug found? Write failing test reproducing it. Follow TDD cycle. Never fix bugs without a test.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: GanyuanRan
• Source: GanyuanRan/Aegis
• License: MIT

Install and usage instructions live in the source repository linked above.