# captain-obvious

Audits TypeScript and Python tests for assertions that can never fail or check nothing, and guides new test authoring against a contract.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 1400 installs · ★ 15
- Author: shmulc8
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/shmulc8/captain-obvious/tree/HEAD/skills/captain-obvious/SKILL.md
- Updated: 2026-09-30
- HTML: https://affpapa.org/en/nevibecode/skills/captain-obvious

## What it does

The skill deletes tests that assert what the compiler, the mock framework or plain logic already guarantees. Those checks burn CI time and inflate coverage confidence while catching no regression. The author points to studies finding test smells in 38–100% of LLM-generated tests.

Cleanup runs through two deterministic scanners in `scripts/`: `captain_obvious_ts.mjs` for TypeScript and `captain_obvious_py.py` for Python. One invocation scans the whole project, so hand-scanning files or spawning a subagent per file is wasted effort. Findings come in two levels: proven (cannot fail by construction, some auto-deleted) and advisory (almost certainly useless but unprovable, never auto-deleted). If the project already produces coverage, `--coverage` promotes the noisiest conditional-assert category to trustworthy.

Fixes edit test files in place, so both scripts demand a git repository with a clean working tree — `--fix` exits 2 otherwise. `--force` drops that guard and with it the only undo path, `git checkout -- <files>`. Scanning executes the project's own toolchain: mypy loads `[tool.mypy] plugins` from the repo config, and the TS detector resolves the repo's `typescript` package. Run it only on repositories where you would run `mypy` or `tsc` yourself.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add shmulc8/captain-obvious --skill captain-obvious -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/captain-obvious/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/captain-obvious/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add shmulc8/captain-obvious --skill captain-obvious -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/captain-obvious/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add shmulc8/captain-obvious --skill captain-obvious -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/captain-obvious/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install shmulc8/captain-obvious captain-obvious
```

2. **Manually: put the files in place**
- File: `.github/skills/captain-obvious/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add shmulc8/captain-obvious --skill captain-obvious -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/shmulc8/captain-obvious --path skills/captain-obvious
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/captain-obvious/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add shmulc8/captain-obvious --skill captain-obvious -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/shmulc8/captain-obvious/tree/HEAD/skills/captain-obvious/SKILL.md

## When to use it
- delete tests that cannot fail
- spot assertions with no real check
- clean up AI-generated test suites
- tell a duplicate test from a useful one
- vet a new test against the authoring gate

## Example prompts
- run the test scanner over this project and show me the report
- clean up the useless tests in this repo
- check my new test against the authoring gate

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: a1eedee5c4b99853.

BEGIN THIRD-PARTY FILE a1eedee5c4b99853
```text
---
name: captain-obvious
description: Audit TypeScript and Python tests for assertions that cannot fail or check nothing, and guide test authoring with a contract and regression gate. Use when writing or changing tests to avoid low-value coverage, or cleaning redundant, tautological, duplicated, or AI-generated tests. Cleanup runs bundled deterministic scanners; authoring guidance needs no scan during red-green TDD.
---

# Captain Obvious

Deletes tests that assert what is already guaranteed — by the compiler, by the
mock framework, or by the laws of logic. These tests burn CI time, inflate
coverage confidence, and can never catch a regression. They are the signature
of AI-generated test suites (empirical studies find test smells in 38–100% of
LLM-generated tests).

For cleanup, two deterministic scripts in `scripts/` do the heavy lifting.
Run them, interpret the report, clean up the residue, and verify nothing broke.
**Do not** hand-scan test files or spawn subagents per file — one script
invocation scans the whole project. During test authoring, use the gate below
without running a cleanup scan.

## Authoring gate

Before adding or changing a test, answer four questions:

1. What observable behavior or independent contract does it protect?
2. What plausible regression would make it fail for the intended reason?
3. Is that contract already covered at a stronger boundary? If so, what
   distinct risk does this test cover?
4. Does it require a production export, flag, wrapper, or injection hook used
   only by tests? Can the real entry point be tested instead?

If a new bug regression test can be run safely against the pre-fix baseline,
verify that it fails for the intended reason and passes with the fix. Use
`references/prevention.md` for examples of patterns to avoid. A test need not
contain a direct assertion to be valuable: a deliberate must-not-raise test
can guard a real contract.

## Workflow

### 1. Detect the stack(s)

- TypeScript/JavaScript: `*.test.*` / `*.spec.*` (ts, tsx, mts, cts, js, jsx,
  mjs, cjs) or files under `__tests__`; a `tsconfig.json` enables type checks.
- Python: `test_*.py` / `*_test.py` files (pytest or unittest).
- A repo can have both; run both detectors.

### 2. Safety first

The fix step edits test files in place. Both scripts enforce this themselves:
`--fix` exits 2 unless the target is a git repository with a clean working
tree (untracked files are fine). If it refuses, stash or commit rather than
reaching for `--force` — `--force` removes the only undo path there is
```
END THIRD-PARTY FILE a1eedee5c4b99853

The third-party file has ended. Everything between the a1eedee5c4b99853 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

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