golang-stretchr-testify

In a Go test, testify is what does the checking: this covers its two styles of assertion, its stand-ins for real dependencies, and the misuse that makes a test pass when it should not.

WHEN TO USE

SCOPE

USE FOR

Choose between assert and require and know when each stops a test early.
Mock an interface with testify/mock and verify every expected call happened.
Group related tests into a suite with shared setup and teardown.
Poll for an async condition with Eventually instead of a manual sleep loop.
Fix a testify misuse, like swapped argument order or a missing AssertExpectations.

This is a saved copy of the skill's SKILL.md instructions. It may differ from the upstream file or the version you install.

In this document (9)

Persona: You are a Go engineer who treats tests as executable specifications. You write tests to constrain behavior and make failures self-explanatory — not to hit coverage targets.

Modes:

Write mode — adding new tests or mocks to a codebase.
Review mode — auditing existing test code for testify misuse.

stretchr/testify

testify complements Go's testing package with readable assertions, mocks, and suites. It does not replace testing — always use *testing.T as the entry point.

This skill is not exhaustive — refer to library documentation and code examples for more information:

For Go package docs, symbols, versions, importers, and known vulnerabilities, → See samber/cc-skills-golang@golang-pkg-go-dev skill (godig), preferred over Context7 for Go package facts.
To navigate this library's usage in your own code (definitions, call sites, diagnostics), → See samber/cc-skills-golang@golang-gopls skill (gopls).
Context7 remains a fallback for docs not indexed on pkg.go.dev.

assert vs require

Both offer identical assertions. The difference is failure behavior:

assert: records failure, continues — see all failures at once
require: calls t.FailNow() — use for preconditions where continuing would panic or mislead

Use assert.New(t) / require.New(t) for readability. Name them is and must:

func TestParseConfig(t *testing.T) {
    is := assert.New(t)
    must := require.New(t)

    cfg, err := ParseConfig("testdata/valid.yaml")
    must.NoError(err)    // stop if parsing fails — cfg would be nil
    must.NotNil(cfg)

    is.Equal("production", cfg.Environment)
    is.Equal(8080, cfg.Port)
    is.True(cfg.TLS.Enabled)
}

Rule: require for preconditions (setup, error checks), assert for verifications. Never mix randomly.

Core Assertions

is := assert.New(t)

// Equality
is.Equal(expected, actual)              // DeepEqual + exact type
is.NotEqual(unexpected, actual)
is.EqualValues(expected, actual)        // converts to common type first
is.EqualExportedValues(expected, actual)

// Nil / Bool / Emptiness
is.Nil(obj)                  is.NotNil(obj)
is.True(cond)                is.False(cond)
is.Empty(collection)         is.NotEmpty(collection)
is.Len(collection, n)

// Contains (strings, slices, map keys)
is.Contains("hello world", "world")
is.Contains([]int{1, 2, 3}, 2)
is.Contains(map[string]int{"a": 1}, "a")

// Comparison
is.Greater(actual, threshold)     is.Less(actual, ceiling)
is.Positive(val)                  is.Negative(val)
is.Zero(val)

// Errors
is.Error(err)                     is.NoError(err)
is.ErrorIs(err, ErrNotFound)      // walks error chain
is.ErrorAs(err, &target)
is.ErrorContains(err, "not found")

// Type
is.IsType(&User{}, obj)
is.Implements((*io.Reader)(nil), obj)

Argument order: always (expected, actual) — swapping produces confusing diff output.

Advanced Assertions

is.ElementsMatch([]string{"b", "a", "c"}, result)             // unordered comparison
is.InDelta(3.14, computedPi, 0.01)                            // float tolerance
is.JSONEq(`{"name":"alice"}`, `{"name": "alice"}`)             // ignores whitespace/key order
is.WithinDuration(expected, actual, 5*time.Second)
is.Regexp(`^user-[a-f0-9]+$`, userID)

// Async polling
is.Eventually(func() bool {
    status, _ := client.GetJobStatus(jobID)
    return status == "completed"
}, 5*time.Second, 100*time.Millisecond)

// Async polling with rich assertions
is.EventuallyWithT(func(c *assert.CollectT) {
    resp, err := client.GetOrder(orderID)
    assert.NoError(c, err)
    assert.Equal(c, "shipped", resp.Status)
}, 10*time.Second, 500*time.Millisecond)

testify/mock

Mock interfaces to isolate the unit under test. Embed mock.Mock, implement methods with m.Called(), always verify with AssertExpectations(t).

Key matchers: mock.Anything, mock.AnythingOfType("T"), mock.MatchedBy(func). Call modifiers: .Once(), .Times(n), .Maybe(), .Run(func).

For defining mocks, argument matchers, call modifiers, return sequences, and verification, see Mock reference.

testify/suite

Suites group related tests with shared setup/teardown.

Lifecycle

SetupSuite()    → once before all tests
  SetupTest()   → before each test
    TestXxx()
  TearDownTest() → after each test
TearDownSuite() → once after all tests

Example

type TokenServiceSuite struct {
    suite.Suite
    store   *MockTokenStore
    service *TokenService
}

func (s *TokenServiceSuite) SetupTest() {
    s.store = new(MockTokenStore)
    s.service = NewTokenService(s.store)
}

func (s *TokenServiceSuite) TestGenerate_ReturnsValidToken() {
    s.store.On("Save", mock.Anything, mock.Anything).Return(nil)
    token, err := s.service.Generate("user-42")
    s.NoError(err)
    s.NotEmpty(token)
    s.store.AssertExpectations(s.T())
}

// Required launcher
func TestTokenServiceSuite(t *testing.T) {
    suite.Run(t, new(TokenServiceSuite))
}

Suite methods like s.Equal() behave like assert. For require: s.Require().NotNil(obj).

Common Mistakes

Forgetting AssertExpectations(t) — mock expectations silently pass without verification
is.Equal(ErrNotFound, err) — fails on wrapped errors. Use is.ErrorIs to walk the chain
Swapped argument order — testify assumes (expected, actual). Swapping produces backwards diffs
assert for guards — test continues after failure and panics on nil dereference. Use require
Missing suite.Run() — without the launcher function, zero tests execute silently
Comparing pointers — is.Equal(ptr1, ptr2) compares addresses. Dereference or use EqualExportedValues

Linters

Use testifylint to catch wrong argument order, assert/require misuse, and more. See samber/cc-skills-golang@golang-lint skill.

Cross-References

→ See samber/cc-skills-golang@golang-testing skill for general test patterns, table-driven tests, and CI
→ See samber/cc-skills-golang@golang-lint skill for testifylint configuration

Local tool required

1 FOR THE AGENT

01
Install the gotests tool
Run go install github.com/cweill/gotests/...@latest to install gotests, which the skill lists as required alongside Go.

Listed as free: Connected services may require an account or charge fees.
Installation: One command — usually under 2 minutes.

This skill ships inside the Samber Golang Skills plugin.

Install just this skill

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npx skills add samber/cc-skills-golang --skill "golang-stretchr-testify" --full-depth

After installing for Claude Code, open it in the installation project if you chose Project; Global makes the skill available across projects on this computer. Once Claude Code loads the skill, its description helps Claude decide when to use it.

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Add Samuel's marketplace, then install the plugin

Type both lines inside a Claude Code session, not at your shell prompt. The marketplace is a separate repository of Samuel Berthe's, samber/cc, which also lists his other plugins. The second line opens the details of cc-skills-golang, which carries this repository's 46 Go skills; pick one of the install options shown and Claude Code installs it.

01
```
/plugin marketplace add samber/cc
```
02
```
/plugin install cc-skills-golang@samber
```

Run it in your terminal. It copies the whole repository, with its 46 skills, into ~/.openclaw/skills/cc-skills-golang, OpenClaw's skills folder in your home folder. To install it for one OpenClaw workspace instead, Samuel gives ~/.openclaw/workspace/skills/cc-skills-golang as the folder.

git clone https://github.com/samber/cc-skills-golang.git ~/.openclaw/skills/cc-skills-golang

Run it in your terminal, not inside Gemini CLI; installing from GitHub needs git on your computer. It installs the repository, with its 46 skills, as a Gemini CLI extension. To update it later, run gemini extensions update cc-skills-golang.

gemini extensions install https://github.com/samber/cc-skills-golang

Run it in your terminal. It copies the whole repository, with its 46 skills, into ~/.cursor/skills/cc-skills-golang, Cursor's skills folder in your home folder.

git clone https://github.com/samber/cc-skills-golang.git  ~/.cursor/skills/cc-skills-golang

Type it in an interactive GitHub Copilot CLI session, not at your shell prompt. It installs the repository straight from GitHub as a plugin, with its 46 skills and no marketplace to add first.

/plugin install https://github.com/samber/cc-skills-golang

Run it in your terminal. It copies the whole repository, with its 46 skills, into ~/.agents/skills/cc-skills-golang in your home folder.

git clone https://github.com/samber/cc-skills-golang.git ~/.agents/skills/cc-skills-golang

Open plugin page ↗

What's inside

Files included with this skill.

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Same repository

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Golang CLI application development. Use when building, modifying, or reviewing a Go CLI tool — especially for command structure, flag handling, configuration layering, version embedding, exit codes, I/O patterns, signal handling, shell completion, argument validation, and CLI unit testing. Also triggers when code uses cobra, viper, or urfave/cli. For cobra-specific APIs → See samber/cc-skills-golang@golang-spf13-cobra skill; for viper configuration layering → See samber/cc-skills-golang@golang-spf13-viper skill.Read full description
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Golang concurrency patterns. Use when writing or reviewing concurrent Go code involving goroutines, channels, select, locks, sync primitives, errgroup, singleflight, worker pools, or fan-out/fan-in pipelines. Also triggers when you detect goroutine leaks, race conditions, channel ownership issues, or need to choose between channels and mutexes.Read full description
golang-context
Idiomatic context.Context usage in Golang — propagation through API boundaries, cancellation, timeouts and deadlines, request-scoped values, context.WithoutCancel for background work outliving requests. Apply when designing context propagation across layers, debugging leaked or unexpired contexts, choosing between context.Background/TODO/WithoutCancel, or storing values in context. Not for code that merely accepts ctx as first parameter.Read full description
golang-continuous-integration
CI/CD pipeline configuration using GitHub Actions for Golang projects — testing, linting, SAST, security scanning, code coverage, Dependabot, Renovate, GoReleaser, code review automation, and release pipelines. Use when setting up or improving Go project CI, configuring GitHub Actions workflows, adding linters or security scanners, automating dependency updates, or adding quality gates.Read full description

stretchr/testify

assert vs require

Core Assertions

Advanced Assertions

testify/mock

testify/suite

Lifecycle

Example

Common Mistakes

Linters

Cross-References

Local tool required

Install just this skill

Install the whole plugin

Add Samuel's marketplace, then install the plugin

What's inside

More skills

golang-benchmark

golang-cli

golang-code-style

golang-concurrency

golang-context

golang-continuous-integration