Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/spumer/i-m-senior-developer/tdd-masternpx skills add spumer/i-m-senior-developer --skill tdd-mastergit clone --depth 1 https://github.com/spumer/i-m-senior-developerWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/spumer/i-m-senior-developer/tdd-master)<a href="https://agentmods.dev/skills/spumer/i-m-senior-developer/tdd-master"><img src="https://agentmods.dev/badge/skills/spumer/i-m-senior-developer/tdd-master.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00083 | $0.01925 |
| Opus 5 | $0.00042 | $0.00962 |
| Sonnet 5 | $0.00017 | $0.00385 |
| Haiku 4.5 | $0.00008 | $0.00193 |
Grade A, and why
tdd-master scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 283 lines — stays where its author put it; the contents beside it link to each section on GitHub.
TDD Master Skill
Test-Driven Development methodology for writing reliable, maintainable code.
When to Activate
This skill activates automatically when:
- Implementing new features (write tests FIRST)
- Fixing bugs (reproduce with failing test FIRST)
- Writing or reviewing tests
- Refactoring code (ensure tests exist)
Core Workflow: Red-Green-Refactor
Step 1: Test List
Before coding, create a list of scenarios:
## Test List for [Feature]
- [ ] Happy path: main scenario
- [ ] Edge case: empty input
- [ ] Edge case: boundary values
- [ ] Error case: invalid input
- [ ] Error case: external service failure
Step 2: RED - Write Failing Test
Write test that defines expected behavior:
def test__{what}__{scenario}__{outcome}():
# Arrange
order = Order(items=[Item(price=1500)])
# Act
discount = calculate_discount(order)
# Assert
assert discount == Decimal('150')
CRITICAL: Predict HOW the test will fail before running.
Step 3: GREEN - Minimal Code
Write MINIMUM code to pass:
- Hardcoded values OK
- Simple if-statements OK
- "Fake it till you make it" OK
Step 4: REFACTOR
After test passes:
- Remove duplication
- Improve naming
- Extract helpers
- Keep tests green
Step 5: REPEAT
Next test from list until complete.
Three Laws of TDD (Uncle Bob)
| # | Law |
|---|---|
| 1 | Cannot write production code without failing test |
| 2 | Cannot write more test than sufficient to fail |
| 3 | Cannot write more production code than sufficient to pass |
FIRST Principles
| Principle | Description |
|---|---|
| Fast | Tests run quickly |
| Independent | No test dependencies |
| Repeatable | Same result everywhere |
| Self-validating | Clear pass/fail |
| Timely | Written BEFORE code |
Fixture Defaults (P0 Pattern)
| Role | Defaults | Example |
|---|---|---|
| FK dependency | Minimal for validity | Campaign(name='Test', status=ACTIVE) |
| Entry point | Maximal for usefulness | create_applicant(with_tilda=True, ...) |
| Edge case | Explicitly marked | create_applicant(with_tilda=False) |
What ships with it
4 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 4d ago First seen · 283 lines · 83 tokens per session scan A ce29d5944a9d
tdd-master is a skill published in the GitHub repository spumer/i-m-senior-developer (11 stars, last pushed 3d ago), licensed MIT. It adds 83 tokens to every session and 1,925 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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