Testing on the Toilet Agent Skill

Apply Google Testing on the Toilet (TotT) rules when writing tests, reviewing a test diff, choosing mocks vs fakes, diagnosing brittle or…

Context cost
4.2k tokensestimated from the bundle, loaded when it triggers
Bundle
2 files · 16.8 kBtext throughout, nothing executable
Licence
not declarednone named by its author
Last change
—no release on file
Servers it uses
Noneruns standalone

What it does

Apply Google Testing on the Toilet (TotT) rules when writing tests, reviewing a test diff, choosing mocks vs fakes, diagnosing brittle or change-detector tests, DAMP vs DRY test structure, SMURF/pyramid layer choice, or flaky time/sleep/shared-fixture tests. Instructs what a good test asserts and what to refuse. Not a Vitest/runner cookbook and not an E2E authoring workflow.

What this skill changes about the agent has not been set out here as a list. Its SKILL.md, shown below, says it in the author’s own words.

securitytestingwriting

The skill itself

A skill is instructions the model reads, so you can see what you are getting: below is the start of its SKILL.md. The front matter loads with every session, the body loads when the skill triggers, and the whole file comes with the install.

SKILL.md7.0 kB · preview
--- name: testing-on-the-toilet ---
11# Testing on the Toilet
12
13Distilled from Google's [Testing on the Toilet](https://testing.googleblog.com/search/label/TotT) episodes (2007–2026). Episode index: [references/episodes.md](references/episodes.md).
14
15Run this loop on every new test and every test you review. Completion: each test that ships would fail on a real behavior bug and would survive a behavior-preserving refactor.
16
17## 1. Change-detector gate
18
19A **change-detector** restates production structure (especially ordered verify of every collaborator call) without checking an observable result. Correct and incorrect implementations pass equally; any rename/extract/reorder fails the suite.
20
21Rewrite it to assert **state, return value, rendered output, or persisted data**. If you cannot name the user-visible contract, **delete the test** and say why. Do not "fix" a refactor by mechanically updating fifty mirrors.
22
23Interaction verify is allowed only when the call itself is the contract (send mail once, do not double-charge, presenter tells the view to show X). If unsure, rewrite to a state/return assertion; if that is impossible, **stop and ask** which observable outcome the test protects.
24
25## 2. Pick the cheapest layer that still has fidelity
26
27Name the bug/risk first. Pick the **topmost** row in the table that can catch it. Escalate a row only when a cheaper layer would miss that risk (state the miss). **SMURF** (Speed, Maintainability, Utilization/cost, Reliability, Fidelity) is the tradeoff language when two rows could both catch it: prefer the cheaper/faster/more reliable one.
28
29| Risk | Layer |
This is a preview of SKILL.md. Download or install the skill to get the whole thing.
In the file
SKILL.md1,063 words
Files2
Licencenot declared
Why you can read it

Nothing in a skill executes. The client loads the text and the model follows it, so a skill can be audited the way a runbook is — by reading it.

What it costs in context

Skills are not billed by the call. They are paid for in context: every token the instructions occupy is a token your code, your diff and your conversation cannot use. Here is what this one takes and when it takes it.

≈110
always loaded
The name and description, so the model knows the skill exists and when to reach for it.
4,090
on trigger
The instruction body and 1 supporting file, read only when the skill fires.
2.1%
of a 200k window
Ten skills this size would take about 21% of the window before you open a file.
050k100k150k200k context window

4.2k tokens, estimated from the bundle at four bytes to the token, held for the rest of the session once it triggers. Heavy. Teams tend to install this one per project rather than globally, and load it only when the job comes up.

Servers bill, skills cost

A server charges by the month. A skill charges once per session, in context, and then keeps charging it for as long as the session lives.

Before and after

The same question, put to the same model twice: once as it comes, and once with these instructions loaded.

No worked example has been published for this skill yet.

The procedure it runs

The procedure has not been set out here step by step. It is in the body of its SKILL.md: the start of it is shown above, and the whole file comes with the install.

Prose, not code

These steps are written for a model to follow, not executed by a runtime. It can still be told to skip one, and it will say so when it does.

Servers it uses

None. This skill calls no MCP servers at all.

Everything it needs is in the instructions, so it works in a project with nothing connected — the model reads the file and changes how it works with what it can already reach.

Its SKILL.md does not declare which tools it asks the agent for, so what it touches is whatever the instructions themselves ask for — read them before you install it.

What it asks for
Writes filesnot declared
Network accessnot declared

This SKILL.md carries no allowed-tools line, so neither is declared. A skill grants no permissions of its own — it can only ask for tools your client already has.

What it will not do

Every skill is narrow, and the useful ones say where they stop. These are the jobs this one is the wrong tool for.

What this skill is not for has not been published here. Nothing is implied by that: it is a section the author has not filled in.

What is in the bundle

2 files, 16.8 kB on disk. A bundle is text throughout: the instructions the model reads, plus the templates it fills in.

  • SKILL.md7.0 kB
  • references/episodes.md9.8 kB
What is not in it

No dependencies and nothing executable: a skill is text the agent reads, so the bundle is 2 files you can review in full before installing.

Install

Installing copies the bundle into your project. Nothing runs at install time — the files sit on disk until the model reads them.

# Testing on the Toilet · 4.2k tokens when loaded · macOS, Linux mkdir -p .claude/skills && t=$(mktemp -d) && curl -fsSL -o "$t/bundle.tar.gz" https://mcprush.com/api/skills/testing-on-the-toilet/bundle.tar.gz && tar -xzf "$t/bundle.tar.gz" -C "$t" && [ -d "$t/testing-on-the-toilet" ] && { [ ! -e .claude/skills/testing-on-the-toilet ] || { mv .claude/skills/testing-on-the-toilet "$t/.previous" && echo "Previous copy moved to $t/.previous"; }; } && mv "$t/testing-on-the-toilet" .claude/skills/ && echo "Installed .claude/skills/testing-on-the-toilet"
On Windows, or any OS with Node 20+
npx mcprush@latest skill add shamashel/testing-on-the-toilet

Windows PowerShell says 'running scripts is disabled on this system'? Run Set-ExecutionPolicy -Scope CurrentUser RemoteSigned once, or type npx.cmd instead of npx (codex.cmd, gemini.cmd, grok.cmd likewise). PowerShell 7 needs neither. Writes to .claude/skills/testing-on-the-toilet/ in the current project. For every project instead, run mkdir -p ~/.claude/skills && t=$(mktemp -d) && curl -fsSL -o "$t/bundle.tar.gz" https://mcprush.com/api/skills/testing-on-the-toilet/bundle.tar.gz && tar -xzf "$t/bundle.tar.gz" -C "$t" && [ -d "$t/testing-on-the-toilet" ] && { [ ! -e ~/.claude/skills/testing-on-the-toilet ] || { mv ~/.claude/skills/testing-on-the-toilet "$t/.previous" && echo "Previous copy moved to $t/.previous"; }; } && mv "$t/testing-on-the-toilet" ~/.claude/skills/ && echo "Installed ~/.claude/skills/testing-on-the-toilet" (macOS, Linux) — or add --global to the npx line. The curl line replaces .claude/skills/testing-on-the-toilet/ only after the download succeeds, so files left there by another skill of the same name, or by an older release, do not mix in. A copy already there is moved aside, not deleted, and the line prints where.

Which clients pick it up on their own

A skill is a folder of text. Most of these read a skills folder and pick it up without being told; the rest take the same folder another way — an upload in the app, a parameter on an API call — and then choose it by its description just the same.

Claude Code.claude/skills/
Claude DesktopCustomize › Skills
ChatGPTSkills › Create › Upload
Cursor.cursor/skills/
VS Code.github/skills/
Codex CLI.agents/skills/
Gemini CLI.gemini/skills/
Grok Build.grok/skills/
Microsoft CopilotSkills › Upload a skill
PerplexityComputer › Skills › Upload a skill
DeepSeek Harness.dsh/skills/
Zed.agents/skills/
Devin Desktop.devin/skills/
Windsurf (legacy).windsurf/skills/
OpenAI Agents SDKInstructions or sandbox Skills
HTTP / APIa request parameter
This release
Versionnot versioned
Publishedno release date on file
PriceFree
Referenceshamashel/testing-on-the-toilet

Versions

Its author publishes no version number, so there is nothing here to pin to: what you install is the folder as it stands today. Instructions change more often than APIs do — a skill can be rewritten entirely without anything it depends on moving.

Pinning

Nothing to pin to: this skill carries no version number of its own. What you install is what the folder holds on the day you install it.

Reviews

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Anybody with an account, one review each. It carries the version that was current when you wrote it, and the publisher may reply once.

Who wrote it

SH
shamashel

Publishes on mcprush.

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