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/djscheuf/agentic-dev-ecosystem-template/write-failing-testnpx skills add djscheuf/agentic-dev-ecosystem-template --skill write-failing-testgit clone --depth 1 https://github.com/djscheuf/agentic-dev-ecosystem-templateWrote 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/djscheuf/agentic-dev-ecosystem-template/write-failing-test)<a href="https://agentmods.dev/skills/djscheuf/agentic-dev-ecosystem-template/write-failing-test"><img src="https://agentmods.dev/badge/skills/djscheuf/agentic-dev-ecosystem-template/write-failing-test.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 | $0.00032 | $0.00822 |
| Opus 5 | $0.00016 | $0.00411 |
| Sonnet 5 | $0.00006 | $0.00164 |
| Haiku 4.5 | $0.00003 | $0.00082 |
Grade A, and why
write-failing-test 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 5d 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 — 120 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Step 1: Select Next Test Case
From your test plan, identify:
- The highest priority unimplemented test
- The specific behavior being tested
- The expected outcome
Step 2: Write the Test Shell
Create the Test with the proper structure. Identify the appripriate language for the component and review an example in one of these files:
- C#:
/reference/test_example.cs - Python:
/reference/test_example.py - TypeScript:
/reference/test_example.ts
Step 3: Implement Arrange Section
Set up the test preconditions:
- Create test data using factories/builders
- Configure mocks for dependencies
- Initialize the system under test (SUT)
Keep setup minimal - only what's needed for THIS test.
Step 4: Implement Act Section
Execute the behavior under test:
- Single method call or action
- Capture the result if needed
- Should be ONE line in most cases
Step 5: Implement Assert Section
Verify the expected outcome:
- Use specific assertions (not just assertTrue)
- One logical assertion per test
- Assert on behavior, not implementation
Step 6: Verify Test Fails
Run the test and confirm:
✓ Test executes without setup errors
✓ Test fails for the RIGHT reason
✓ Failure message is clear and helpful
✗ Test should NOT pass yet
If test passes → Something is wrong:
- Test may not be testing new behavior
- Code already exists
- Test has a bug
// TODO - Add Run-Test Skill specific to the project's testing framework, supporting that projects structure
Step 7: Document the Failure
Update the test plan and mark the test as "failing".
Step 8: Write the Sentinel File
- create a sentinel file in the
.processdirectory, named{skill-name}.done.json. - the sentinel file will follow @/schema/sentinel.schema.json.
- set the task field to "{skill-name}".
- the verify_params of the sentinel file will follow @/schema/verify-params.schema.json.
- set the verify_params as follows:
- set "test_cases_path" to the path of the test cases file relative to repo root.
- set "failing_test_path" to the path of the failing test file relative to repo root.
- set "failing_test_name" to the name of the failing test.
What ships with it
6 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.
- 5d ago First seen · 120 lines · 32 tokens per session scan A 2a195ecddc4d
write-failing-test is a skill published in the GitHub repository djscheuf/agentic-dev-ecosystem-template (12 stars, last pushed today), licensed MIT. It adds 32 tokens to every session and 822 once invoked, about $0.0002 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 2026-08-30.
Other skills, from other repositories
engram-testing-coverage
TDD and coverage standards for Engram. Trigger: When implementing behavior changes in any package.
nunit-testing
Use when writing or modifying tests in NUnit's own test projects, or when making a behavioral change to production code that needs test coverage. Covers test structure, attribute choice, helper visibility, platform guards, and which test projects are real.
tdd
Test-driven development. Use when the user wants to build features or fix bugs test-first, mentions "red-green-refactor", or wants integration tests.
strict-tdd
Strict RED->GREEN->REFACTOR test-driven development with enforcement. Never write production code before a failing test. Atomic commits per TDD cycle.
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…
conductor-implement
Execute tasks from a track's implementation plan following TDD workflow.