# Tdd

> Use for writing the first right-reason failing test for new or changed observable behaviour, then red-green-refactor. Not for behaviour-preserving structure, diagnosis-only, or delivery; use refactor, diagnose, or implement.

- **Type:** Skill
- **Install:** `agentstack add skill-mblauberg-provenant-tdd`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [mblauberg](https://agentstack.voostack.com/s/mblauberg)
- **Installs:** 0
- **Category:** [Agent Skills](https://agentstack.voostack.com/c/agent-skills)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [mblauberg](https://github.com/mblauberg)
- **Source:** https://github.com/mblauberg/provenant/tree/main/skills/tdd

## Install

```sh
agentstack add skill-mblauberg-provenant-tdd
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# Test-driven development

```text
NO NEW OR CHANGED OBSERVABLE BEHAVIOUR WITHOUT A RIGHT-REASON FAILURE FIRST
```

Never delete or overwrite unknown, pre-existing or user-authored work to create
a red state. If this run wrote production code before the test, preserve its
patch, remove only the exact run-owned hunks when authorised, witness the
right-reason failure, then reapply and minimise them. Existing code gets a
regression or characterisation seam before repair. Deliberate throwaway
prototypes, generated code and configuration may use an explicitly recorded
exception; deadline pressure is not one.

## Red -> green -> refactor

1. **Red:** write one test for one observable behaviour through the public
   interface. Name it like a specification. Run it and confirm it fails because
   the behaviour is missing, not from setup, import or typo. A test that passes
   immediately needs sharpening.
2. **Green:** write only the simplest production change that passes. Avoid
   speculative options and unrelated cleanup. Run the focused test each cycle,
   affected checks at tranche boundaries, and the full required suite at the
   enclosing verification gate; output must be clean.
3. **Refactor:** only while green, remove duplication, improve names and deepen
   modules. Rerun tests after each structural step.

Work vertically: test -> implementation -> repeat. Start with one tracer bullet
through the full path, then add behaviours from what each cycle reveals. Never
write an imagined horizontal test batch before implementation. Prioritise
critical paths and complex logic.

## Test boundaries

Test what callers observe, not private methods, internal call order or data
shape. A valid test survives an internal refactor. Verify outcomes through the
public interface rather than querying side channels. See
[tests.md](references/tests.md).

Mock only system boundaries: external APIs, time/randomness and, when needed,
filesystem/database. Never mock owned internal collaborators to make a test
pass; inject a narrow boundary instead. See [mocking.md](references/mocking.md)
and [interface-design.md](references/interface-design.md).

Hard-to-test code is design evidence: accept dependencies, return results
instead of hiding effects, and prefer deep modules with small interfaces. On
green, use [deep-modules.md](references/deep-modules.md) and
[refactoring.md](references/refactoring.md); do not smuggle redesign into green.

## Advance gate

Before the next behaviour confirm: public observable contract; witnessed
right-reason failure; minimal passing code; focused and broader checks green;
no dirty output; and resilience to internal refactoring.

For a bug, first reproduce the exact failure as the regression test, watch it
fail, then repair and watch it pass. If no correct seam reaches the bug, route
to `diagnose`; do not bless a shallow test. `implement` owns independent review,
repair loops, documentation and user acceptance.

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [mblauberg](https://github.com/mblauberg)
- **Source:** [mblauberg/provenant](https://github.com/mblauberg/provenant)
- **License:** MIT

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-mblauberg-provenant-tdd
- Seller: https://agentstack.voostack.com/s/mblauberg
- Browse the marketplace: https://agentstack.voostack.com/browse

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