Implementing

<EXTREMELY-IMPORTANT> This skill is rigid. Every sub-function must complete the full loop: TDD → Review → Sub-function Full Testing. Skipping any step = unverified code entering the main branch.

If writing-plans already produced a task group breakdown, execute them group by group. If this is a bug fix (no writing-plans), use Bug Fix Mode.

If you find yourself thinking "this feature is too simple, let me just quickly go through it" — read Red Flags. </EXTREMELY-IMPORTANT>

Implementing: TDD → Review → Testing

Skill Type: Rigid

Follow strictly. Every sub-function goes through the full loop; after all pass, proceed to Full-Scenario Integration Testing. No skipping.

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Core Philosophy

Implementation != writing code. Implementation = writing code + proving it correct + proving it didn't break anything else.

Full loop for one sub-function:
  TDD(RED→GREEN→REFACTOR) → subagent 8-Dimension Review (P0/P1 cleared) → Sub-function Full Testing
                                                                                    │
After all sub-functions pass:                                                       │
  Full-Scenario Integration Testing (cross-feature combination scenarios) ──────────┘

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Pre-Flight Checks

#	Check Item	Notes
1	writing-plans produced a task list?	Each task broken down into RED→GREEN→REFACTOR
2	brainstorming produced test scenarios?	2 layers x 4 scenario types (isolation/boundary/concurrency/exception)
3	roadmap §4 consulted?	Confirm no wheel reinvention
4	L2 general experience searched?	Subagent search recommended

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Per-Function Loop (each task group executed independently)

writing-plans task list
       │
       ▼
┌─────────────────────────────────────────────────┐
│ For each task group X:                          │
│                                                 │
│ Step 1: TDD                                     │
│   X-R  RED: write test first → confirm FAIL      │
│   X-G  GREEN: minimal impl + L4 signature verify → PASS │
│   X-F  REFACTOR: clean up → keep PASS            │
│                                                 │
│ Step 2: Subagent 8-Dimension Review (parallel dispatch) │
│   → aggregate → clear P0/P1 → record in roadmap §5      │
│                                                 │
│ Step 3: Sub-function Full Testing (subagent parallel)   │
│   → full boundary/null/concurrency/exception coverage    │
│   → all pass → record in roadmap §5              │
│                                                 │
│ Any step fails → fix → retry from the failed step│
└─────────────────────────────────────────────────┘
       │
       ▼
All task groups pass → Full-Scenario Integration Testing → enter closing-the-loop

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Step 1: TDD Cycle

RED: Write Test First

→ Load from brainstorming test scenarios (2 layers x 4 types)
→ ≥2 test methods per type, ≥8 total
→ Method names express intent: should_xxx_when_yyy
→ Run tests → confirm all FAIL (red)
→ If a test passes immediately → the test is written incorrectly
→ git commit -m "RED: {scenario description}"

GREEN: Minimal Implementation

→ Write only the code needed to make current tests pass (YAGNI)
→ ★ L4 Signature Verification: Read at least 3 called key methods, confirm signatures match
→ Run tests → confirm all PASS (green)
→ git commit -m "GREEN: {implementation description}"

L4 Signature Verification (mandatory):

Calling UserService.getById(Long id)?
→ Read UserService.java → return type? exception declarations? parameter order?
→ LLM method signatures recalled from memory have ~15% chance of being wrong.
   30 seconds of verification > 30 minutes of debugging.

REFACTOR: Clean Up

→ Eliminate duplication (DRY), improve naming, extract constants
→ Run tests after each change (keep green)
→ git commit -m "REFACTOR: {cleanup description}"

Bug Fix TDD Pattern

bug report → RED (write reproduction test, confirm failure) → GREEN (apply fix, test turns green)
→ same-pattern search (Grep for identical bug pattern, fix all) → REFACTOR

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Step 2: Subagent 8-Dimension Parallel Review

After TDD REFACTOR commit, immediately dispatch 8 read-only reviewer subagents (parallel).

P0/P1 must be cleared to zero before entering Step 3.

Severity Definitions

Level	Meaning	Example	Action
P0 Critical	Security vulnerability, data loss, guaranteed crash	SQL injection, unconditional NPE, deadlock	Block
P1 Major	Logic error, regression risk, missing boundary	User A accessing User B data, transaction boundary error	Block
P2 Minor	Pattern deviation, duplicate code, naming issues	Unused existing utility, swallowed exception	Should fix
P3 Suggestion	Better approach, optional optimization	Stream over for-loop	Optional

8 Reviewers Dispatched in Parallel

All 8 reviewers dispatched simultaneously. Use 5-Segment Prompt, read-only.

#	Reviewer	Focus	Severity Range
1	Correctness Deep-Dive	Per-code-path logic verification, condition coverage, type casting	P0-P3
2	Null Safety/Boundaries	Null propagation chain, collection bounds, numeric overflow, string boundaries	P0-P2
3	Security Audit	SQL injection, privilege escalation, sensitive data exposure, input validation	P0-P1
4	Concurrency Safety	Race conditions, thread safety, idempotency, lock ordering	P0-P1
5	Error Handling	Exception coverage completeness, empty catch, degradation, timeout	P0-P2
6	Performance/Resources	N+1 queries, connection leaks, unnecessary object creation	P1-P3
7	Regression Risk	Call chain impact, API compatibility, database migration	P1-P2
8	Contract Verification	API signature/DTO field consistency with design outline/roadmap §3	P1-P2

5-Segment Reviewer Prompt Template

SCOPE: All source files in this change (new and modified)

GOAL: {Select the corresponding GOAL from the 8 reviewers above}

CONSTRAINTS:
  - Don't trust method names — open the called method's source to verify actual behavior
  - Reference every issue with specific file:line

DO NOT:
  - Do not modify code (you are a read-only reviewer)
  - Do not review content outside your assigned dimension
  - Do not propose "better but out of scope" suggestions

RETURN:
  - Issue list (file:line + specific problem + P0/P1/P2/P3)
  - If no issues: "{Dimension}: Pass"

Main Agent Aggregation

Step 1: Deduplicate → same issue found by multiple reviewers, merge into one
Step 2: Prioritize → P0 > P1 > P2 > P3
Step 3: Decide → P0+P1 = 0 → proceed to Step 3 (Sub-function Full Testing)
               → P0+P1 > 0 → implement fixes → re-review only affected dimensions (≤3 rounds)
Step 4: Record → review summary written to roadmap §5

Review Loop (≤3 Rounds)

Each round only fixes P0/P1, no opportunistic refactoring. Only re-dispatch affected reviewers. Round 3 still has P0/P1 → STOP, main agent intervenes to decide.

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Step 3: Sub-function Full Testing

After P0/P1 cleared to zero, dispatch test subagents in parallel covering 4 scenario types:

Dispatch 4 test subagents in parallel (Agent tool):

Test A — Boundary Conditions:
  Null parameters, null, empty list, max/min values, excessively long strings
  RETURN: pass/fail + test results

Test B — Isolation/Multi-User:
  User A's data ≠ User B's, permission boundaries across roles
  RETURN: pass/fail + test results

Test C — Concurrency/Race Conditions:
  Simultaneous operation conflicts, duplicate submission, idempotency
  RETURN: pass/fail + test results

Test D — Exception Paths:
  Dependent service unavailable, timeout, illegal arguments
  RETURN: pass/fail + test results

All pass → this sub-function is complete, record in roadmap §5. Any fails → fix → re-dispatch that test subagent.

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Full-Scenario Integration Testing (after all sub-functions pass)

Cross-feature combination scenario testing (parallel dispatch):

Scenario 1: Complete business flow (end-to-end)
Scenario 2: Multi-user concurrent operations across different features
Scenario 3: Cross-feature data passing/state change chain
Scenario 4: Combined exception scenarios (Feature A fails → Feature B degrades)

All scenarios pass → enter closing-the-loop.

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Bug Fix Mode

When there are no writing-plans outputs (bug fix), use this mode.

Must go through brainstorming first (workflow requires brainstorming → implementing(Bug Mode)). brainstorming should have already written the bug analysis + fix outline to the roadmap. If brainstorming was not executed, implementing must complete this mini version and record to roadmap before writing any code:

Pre-flight: Confirm brainstorming is complete (bug analysis + fix outline written to roadmap §5)
  If not → first complete mini brainstorming:
    1. Clarify bug symptoms and impact scope
    2. Identify involved classes/methods (git log recent changes)
    3. Fix approach (1-3 sentences)
    4. ★ Record in roadmap §5 (date + bug description + files involved + fix approach)
       ↓ only then proceed to RED

RED (reproduction test, confirm bug exists)
    → GREEN (minimal fix, test turns green)
    → REFACTOR (search for same bug pattern, fix all occurrences)
    → Subagent Review (8 dimensions, emphasis on Regression Risk)
    → Sub-function Full Testing (4 scenario types)
    → closing-the-loop

Not writing a reproduction test first = you don't know whether you "fixed it" or it "just happened to stop erroring." Not writing to roadmap first = the next person hitting a similar bug starts from scratch.

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Subagent Usage Principles

Phase	Tool Permission	Parallel Count	Notes
TDD (RED/GREEN/REFACTOR)	Full	1	Main agent executes or dispatches 1 implementer
8-Dimension Review	Read-only	8 parallel	Independent reviewers, no cross-interference
Sub-function Full Testing	Read-only	4 parallel	One per scenario type
Full-Scenario Integration Testing	Read-only	4 parallel	Cross-feature scenarios

Git operations (commit, branch management, etc.) are recommended to be delegated to subagents. The main agent is responsible for roadmap writing and architectural decisions.

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Test Anti-Patterns

Anti-Pattern	Correct Approach
Tests depend on external services	Mock external dependencies
Tests have ordering dependencies	Each test is independent
Method names don't express intent	should_throw_when_email_is_empty()
Only testing happy path	Cover null, empty list, max values
Writing tests for coverage metrics	Test behavior, not implementation details
Writing tests after code is done	Write tests first — the design thinking in RED phase is half of TDD's value

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Red Flags — You Are Skipping Quality Assurance

What You Think	The Truth
"This feature is too simple, no need for review"	Simple code has boundary bugs too. Simple = review is faster = no excuse.
"I can review it myself, no need for 8 reviewers"	You have blind spots reviewing your own code. Independent reviewers don't carry the implementer's assumptions.
"The change is tiny, just quickly go through it"	One wrong line can cost 2 hours of debugging. Small changes still need 8-Dimension Review.
"8 reviewers is too many, 3-4 is enough"	The 4 dimensions you skip are the escape hatches for bugs.
"Write the implementation first, add tests later"	Tests added later become "verify implementation" not "verify behavior." Half of TDD's value is in the RED phase.
"I'll just run integration tests manually"	Manual testing = tested this time, forgotten next time. Automation means reproducible every time.
"The reviewer flagged an issue but I think it's fine"	Don't override the reviewer. Independent judgment covers your blind spots.

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Completion Criteria

Per sub-function completion:

• TDD Triplet complete (RED→GREEN→REFACTOR, one git commit each)
• L4 Signature Verification complete (≥3 key method signatures verified against source)
• 8-Dimension Review complete (P0=0, P1=0)
• Sub-function Full Testing passed (4 scenario types fully covered)
• Review results and test coverage recorded in roadmap §5

After all sub-functions complete:

• Full-Scenario Integration Testing passed (4 cross-feature scenarios)
• All tests green
• Enter closing-the-loop