test-driven-development

# Execute

→ 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.
  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`.

## When to Use

New features, bug fixes, refactoring, behavior/logic changes, interface/data contract changes, cross-module or shared module changes, 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:

```text
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.

## 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.

## 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.

```text
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`.

```text
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 <aegis-workspace-helper> init --root <target-project-root>`) when it
is available. If the task needs a process trail under `work/`, prefer
`python <aegis-workspace-helper> new-work --root <target-project-root> ...`
so the intent, checkpoint, drift, and evidence paths are indexed and
structurally checkable:

```text
docs/aegis/
  README.md
  INDEX.md
  BASELINE-GOVERNANCE.md
  adr/
  baseline/
  specs/
  plans/
  work/YYYY-MM-DD-<task-slug>/
    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 s