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Agent skill

Overview

by onsi in onsi/gomega

The Gomega mental model for writing assertions in Go — the Expect/Ω notation, matchers-are-values, the multi-return error idiom, synchronous vs asynchronous (Eventually/Consistently) assertions, and…

MITAuto-check passedDevelopment

Install Overview

skills CLI
$ npx skills add onsi/gomega --skill overview -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install onsi/gomega overview --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/onsi/gomega.git skills-src && mkdir -p .claude/skills && cp -r skills-src/plugins/gomega/skills/overview .claude/skills/overview && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
overview
GitHub stars
2.4k
Token cost
~1.1k tokens
SKILL.md length
414 words
Files
1
Skills in repo
12
Repo updated
First seen
Licence
MIT

At a glance

The Gomega mental model for writing assertions in Go — the Expect/Ω notation, matchers-are-values, the multi-return error idiom, synchronous vs asynchronous (Eventually/Consistently) assertions, and…

  • Tasks that involve Async programming
  • SKILL.md covers The shape of every assertion, Three things to internalize, Pick the most specific matcher and Where to go next
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Overview is an agent skill from onsi/gomega. The Gomega mental model for writing assertions in Go — the Expect/Ω notation, matchers-are-values, the multi-return error idiom, synchronous vs asynchronous (Eventually/Consistently) assertions, and a map of the whole library including the gstruct/ghttp/gexec/gbytes/gleak/gmeasure sub-libraries. Use this first when you start writing or reviewing Gomega assertions, or to decide which gomega: skill to reach for. Routes to every other gomega: skill.

Its SKILL.md is about 1.1k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Development, covering Async programming. The repository describes itself as: Ginkgo's Preferred Matcher Library. The licence is MIT.

When your agent uses it

  • Tasks that involve Async programming

Example prompts

  • “/overview”

What it can do on your machine

Read from SKILL.md and the folder at commit 37fa900. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md (its code samples are go).

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    Links to these hosts (documentation or services it may open):

    • github.com
    • onsi.github.io

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Overview loads about 1.1k tokens when it runs. Until then it costs about 115 tokens; SKILL.md has 414 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~115
When it runs · the whole SKILL.md, loaded when a task matches
~1.1k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from onsi/gomega at commit 37fa900, republished under its MIT licence (© onsi). 414 words, ~1,126 tokens.

Download SKILL.mdSave it as .claude/skills/overview/SKILL.md (or your agent's skills folder).
name
overview
description
The Gomega mental model for writing assertions in Go — the Expect/Ω notation, matchers-are-values, the multi-return error idiom, synchronous vs asynchronous (Eventually/Consistently) assertions, and a map of the whole library including the gstruct/ghttp/gexec/gbytes/gleak/gmeasure sub-libraries. Use this first when you start writing or reviewing Gomega assertions, or to decide which gomega:* skill to reach for. Routes to every other gomega:* skill.

Gomega: the mental model

Gomega is a matcher/assertion library for Go. It pairs best with the Ginkgo test framework but works with any Go test. The canonical narrative docs at https://onsi.github.io/gomega/ are the source of truth; this skill is the orientation and the other skills go deep.

Conventionally you dot-import Gomega so Expect, Equal, Eventually, etc. are unqualified:

go
import (
	. "github.com/onsi/gomega"
	. "github.com/onsi/ginkgo/v2" // if using Ginkgo
)

The shape of every assertion

go
Expect(ACTUAL).To(MATCHER)        //  Expect(x).To(Equal(3))
Expect(ACTUAL).NotTo(MATCHER)
  • ACTUAL (left) is anything — the value under test.
  • MATCHER (right) must satisfy the GomegaMatcher interface. Gomega's matchers (Equal(3), HaveLen(2), …) are just functions that return a matcher value — so you can store, pass, and compose them. → gomega:matchers, gomega:composing-matchers.
  • Ω(ACTUAL).Should(MATCHER) / .ShouldNot(...) is the exact equivalent in the Ω notation (⌥z on macOS). To/Should and NotTo/ToNot/ShouldNot are interchangeable syntactic sugar — pick one notation and stay consistent.

Three things to internalize

1. The multi-return error idiom. Expect/Ω accept multiple arguments; the match runs against the first, and fails unless all later arguments are nil/zero. This collapses Go's (value, error) pattern:

go
Expect(DoSomethingHard()).To(Equal("foo"))   // passes only if return is ("foo", nil)
Expect(DoSomethingSimple()).To(Succeed())     // for funcs returning only error

Use .Error() to assert on the trailing error of a multi-return func while ignoring the rest. → gomega:assertions.

2. Failures go through a fail handler. Gomega calls a registered handler on failure. With Ginkgo, RegisterFailHandler(Fail) (auto-generated by ginkgo bootstrap). With plain testing, use g := NewWithT(t) and call g.Expect(...). → gomega:assertions.

3. Synchronous vs asynchronous. Expect asserts now. Eventually/Consistently poll a value, function, or g Gomega callback until a matcher passes (or keeps passing). Async is its own world with timeouts, contexts, and bail-out signals. → gomega:async.

Show full SKILL.md (172 more words)Show less

Pick the most specific matcher

The single biggest quality lever: prefer the matcher that says what you mean. Expect(err).To(MatchError(...)) over Expect(err.Error()).To(Equal(...)); Expect(xs).To(ConsistOf(...)) over Expect(len(xs)).To(Equal(3)). Specific matchers produce far better failure messages. Browse the full catalog before reaching for Equal — Gomega has a deep, expressive matcher library. → gomega:matchers.

Where to go next

Core mechanics

  • Synchronous assertions — Expect/Ω, error handling, Succeed/HaveOccurred, negation, annotations, output tuning, asserting inside helpers → gomega:assertions
  • Asynchronous assertions — Eventually/Consistently, polling functions & g Gomega callbacks, contexts, timeouts, StopTrying/TryAgainAfter → gomega:async

Matchers

  • The full catalog (terse, grouped — start here to discover matchers) → gomega:matchers
  • Composing — And/Or/Not, SatisfyAll/SatisfyAny, WithTransform, HaveField, HaveValue → gomega:composing-matchers
  • Writing your own — the GomegaMatcher interface and gcustom → gomega:custom-matchers

Sub-libraries (each its own import; reach for them by task)

  • gstruct — deep, partial matching of nested structs, slices, and maps → gomega:gstruct
  • ghttp — a test server for asserting on and stubbing HTTP clients → gomega:ghttp
  • gexec — build, run, signal, and assert on external processes → gomega:gexec
  • gbytes — assert on streaming io buffers with the Say matcher → gomega:gbytes
  • gleak — detect leaked goroutines → gomega:gleak
  • gmeasure — benchmark and measure code → gomega:gmeasure

© onsi, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in plugins/gomega/skills/overview of onsi/gomega.

Open the folder on GitHubat commit 37fa900

Compare with similar skills

Overview next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Overview compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Overview this skillonsi/gomega2.4k—~1.1kAutomated safety check: PassMIT
YugabyteDB ASH Instrumentationyugabyte/yugabyte-db11k—~4.5kAutomated safety check: PassCustom licence
Mirage VFS Adapter Authoringstrukto-ai/mirage3.7k—~2.4kAutomated safety check: PassApache-2.0
Golang Patternsantoniopaya22/go-rest-template1729 repos~3.5kAutomated safety check: PassNone
Rust Async Patternsdiodeme/Gold-Band1439 repos~3.1kAutomated safety check: PassAGPL-3.0
Swift Concurrencyhenrypldev/react-native-nitro-mlx1003 repos~3.1kAutomated safety check: PassMIT

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More from onsi/gomega

All 12 skills in this repo

  • Assertions

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    Write correct synchronous Gomega assertions — Expect/Ω notation, the To/NotTo/ToNot/Should/ShouldNot equivalences, the multi-return error idiom, Succeed vs HaveOccurred, the .Error() chaining form…

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  • Custom Matchers

    onsi/gomega

    Writing your own Gomega matchers — the GomegaMatcher interface (Match/FailureMessage/NegatedFailureMessage), gcustom.MakeMatcher with message templates and template data, the format package helpers…

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  • Gbytes

    onsi/gomega

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  • Gexec

    onsi/gomega

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Categories

Questions about Overview

What does Overview do?

The Gomega mental model for writing assertions in Go — the Expect/Ω notation, matchers-are-values, the multi-return error idiom, synchronous vs asynchronous (Eventually/Consistently) assertions, and…. Overview is an agent skill from onsi/gomega. The Gomega mental model for writing assertions in Go — the Expect/Ω notation, matchers-are-values, the multi-return error idiom, synchronous vs asynchronous (Eventually/Consistently) assertions, and a map of the whole library including the gstruct/ghttp/gexec/gbytes/gleak/gmeasure sub-libraries.

When should I use Overview?

Overview fits situations like: tasks that involve Async programming.

How do I install Overview in Claude Code?

Run `npx skills add onsi/gomega --skill overview -a claude-code`. Or copy the skill folder (plugins/gomega/skills/overview in onsi/gomega) into .claude/skills/overview in your project. Claude Code loads it when a task matches its description.

How do I install Overview in Codex?

Run `npx skills add onsi/gomega --skill overview -a codex`. Or copy the skill folder (plugins/gomega/skills/overview in onsi/gomega) into .agents/skills/overview in your project. Codex loads it when a task matches its description.

Can I use Overview in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add onsi/gomega --skill overview -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/overview, .gemini/skills/overview, .github/skills/overview and .opencode/skills/overview in your project.

What does Overview need to run?

SKILL.md names no scripts, command-line tools or credentials: Overview is instructions for the agent only.

Does Overview access the network?

SKILL.md names 2 domains. As links in the text: github.com and onsi.github.io. This is read from the text; nothing was executed.

Is Overview safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Overview use?

Overview is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Overview use?

About 1.1k tokens (SKILL.md is roughly 4.5k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Overview?

Skills that share tags, products or a category with Overview: YugabyteDB ASH Instrumentation (yugabyte/yugabyte-db, 11k stars), Mirage VFS Adapter Authoring (strukto-ai/mirage, 3.7k stars), Golang Patterns (antoniopaya22/go-rest-template, 172 stars) and Rust Async Patterns (diodeme/Gold-Band, 143 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Overview?

onsi (a GitHub user) maintains it in onsi/gomega, which has 2,357 GitHub stars. The repository holds 12 skills in this directory. The repository was last updated on September 24, 2026.

Source: onsi/gomega on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.