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,

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 : Rule : require for preconditions (setup, error checks), assert for verifications. Never mix randomly. Core Assertions Argument order : always (expected, actual) — swapping produces confusing diff output. Advanced Assertions 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](./references/mock.md). testify/suite Suites group related tests with shared setup/teardown. Lifecycle Example 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

golang-stretchr-testify