golang-stretchr-testify

by samber

Comprehensive guide to stretchr/testify for Golang testing. Covers assert, require, mock, and suite packages in depth. Use when writing tests with testify, creating mocks, setting up test suites, or choosing between assert and require. Covers testify assertions, mock expectations, argument matchers, call verification, suite lifecycle, and advanced patterns like Eventually, JSONEq, and custom matchers. Apply when the codebase imports github.com/stretchr/testify. npx skills add https://github.com/samber/cc-skills-golang --skill golang-stretchr-testify Download ZIPGitHub2.4k 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. Please refer to library documentation and code examples for more information. Context7 can help as a discoverability platform. For Go package docs, versions, symbols, and known vulnerabilities, → See samber/cc-skills-golang@golang-pkg-go-dev skill.

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).

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