Getting it into your agent
This one installs as part of its plugin. Adding the marketplace and installing the plugin brings it with everything else the plugin ships.
/plugin marketplace add MadAppGang/magus/plugin install devWrote 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/madappgang/magus/test-driven-development)<a href="https://agentmods.dev/skills/madappgang/magus/test-driven-development"><img src="https://agentmods.dev/badge/skills/madappgang/magus/test-driven-development/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/madappgang/magus/test-driven-development"><img src="https://agentmods.dev/badge/skills/madappgang/magus/test-driven-development.svg" alt="Reviewed on agentmods" width="80" 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 5.1 | $0.00058 | $0.04002 |
| Opus 5.5 | $0.00023 | $0.01601 |
| Sonnet 5.5 | $0.00012 | $0.00800 |
| Haiku 4.5 | $0.00006 | $0.00400 |
Grade A, and why
test-driven-development 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 25d 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.
This is a copy
94% identical to test-driven-development — 13 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 530 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Test-Driven Development (TDD)
Iron Law: "NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST"
When to Use
Use this skill when:
- Writing new functions, methods, or classes
- Adding features to existing code
- Fixing bugs (write test that reproduces bug first)
- Refactoring code (tests verify behavior preservation)
- Implementing API endpoints or business logic
- Creating UI components with testable behavior
Red Flags (Violation Indicators)
Watch for these patterns that indicate TDD violations:
- Implementation First - Writing production code before any test exists ("I'll write the function, then add tests")
- "Tests After" Promise - Planning to write tests later ("Let me implement this quickly, I'll add tests after")
- "Same Purpose" Rationalization - Claiming manual testing is equivalent ("I tested it manually, that's the same thing")
- Skipping "Simple" Code - Avoiding tests for "obvious" logic ("This function is too simple to test")
- Happy Path Only - Writing tests only for success cases, ignoring errors ("The normal case works, that's enough")
- No Test for Changes - Modifying code without adding corresponding test ("Just a small change, doesn't need a test")
- "Just a Small Fix" - Bypassing TDD for "quick fixes" ("It's only one line, I don't need a test")
Violation Detection: If you find yourself saying "I'll test this after I get it working," you're violating TDD.
RED-GREEN-REFACTOR Cycle
TDD follows a strict 3-phase workflow:
Phase 1: RED (Write a Failing Test)
Objective: Specify desired behavior through a test that fails
Steps:
- Write the test first - Before any production code exists
- Define expected behavior - What should the code do?
- Use API you wish existed - Test the interface you want
- Run the test - Verify it fails (if it passes, you didn't test new behavior)
- Check failure reason - Ensure it fails for the right reason (missing code, not syntax error)
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.
- 25d ago Changed 986af4ebfb8c
- 1mo ago First seen · 530 lines · 58 tokens per session scan A fb4bca7ba71c
test-driven-development is a skill published in the GitHub repository MadAppGang/magus (13 stars, last pushed today), licensed MIT. It adds 58 tokens to every session and 4,002 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 94% identical to test-driven-development, differing in 13 lines, and is treated as a copy.
Other skills, from other repositories
engram-testing-coverage
TDD and coverage standards for Engram. Trigger: When implementing behavior changes in any package.
conductor-implement
Execute tasks from a track's implementation plan following TDD workflow.
principle-test-behavior-not-implementation
Apply when you write, change, or keep a test. Assert what the code's users can observe, so that the test fails when that behavior breaks and keeps passing when only the internals change.
iterative-development
TDD iteration loops using Claude Code Stop hooks - runs tests after each response, feeds failures back automatically.
python
Python development with ruff, mypy, pytest - TDD and type safety.
tdd
This skill should be used when the user wants to implement features or fix bugs using test-driven development. Enforces the RED-GREEN-REFACTOR cycle with vertical slicing, context isolation between test writing and implementation, human checkpoints, and auto-test feedback loops. Uses multi-agent orchestration with the…