go-testing-patterns

name	go-testing-patterns
description	Use when writing or reviewing Go tests - standard testing package, table-driven tests, subtests, test helpers, httptest, benchmarks, fuzz testing, and interface-based mocking.

Go Testing Patterns

Standard Go testing package patterns and common libraries. For shared test quality principles (philosophy, smells, mocking decisions), see testing-patterns.

Reference Routing

Need	Reference File	Sections to Read
Go testing patterns	${CLAUDE_SKILL_DIR}/../testing-patterns/references/go-testing-patterns.md	Full file (~420L, manageable)
Behavior vs implementation	${CLAUDE_SKILL_DIR}/../testing-patterns/references/test-philosophy.md	## The Fundamental Shift + ## Four Core Principles
Flaky/brittle tests	${CLAUDE_SKILL_DIR}/../testing-patterns/references/test-smells.md	## The Six Major Test Smells (relevant subsection)
Mock usage decisions	${CLAUDE_SKILL_DIR}/../testing-patterns/references/mocking-strategies.md	## The Mocking Decision Framework
AAA pattern/naming	${CLAUDE_SKILL_DIR}/../testing-patterns/references/test-structure.md	## The AAA Pattern + ## Test Naming Conventions
Test data strategy	${CLAUDE_SKILL_DIR}/../testing-patterns/references/test-data.md	## Factories + ## Builders

How to read sections: Grep for heading to find line number, Read with offset+limit.

Go Assertion Quick Reference

Use	Instead Of	Why
t.Fatalf("got %v, want %v", got, want)	t.Errorf for preconditions	Stops test when continuing is meaningless
require.NoError(t, err)	if err != nil { t.Fatal(err) }	Concise with testify (optional)
t.Run(tt.name, func(t *testing.T) {...})	Flat loop body	Isolates cases, enables -run filtering
t.Helper()	Nothing	Failures point to caller, not helper
t.Setenv("KEY", "val")	os.Setenv + defer restore	Auto-restored, goroutine-safe
t.TempDir()	os.MkdirTemp + defer remove	Auto-cleaned after test
t.Cleanup(fn)	defer fn()	Runs even on t.FailNow/t.Fatal
httptest.NewServer(handler)	Real HTTP calls	Fast, deterministic, no network

Go Red Flags

Pattern	Why Harmful	Fix
Missing t.Helper() in helpers	Wrong failure location	Add as first line in helper functions
os.Setenv without t.Setenv	Env leaks between tests	Use t.Setenv() (Go 1.17+)
Table tests without t.Run	Can't isolate or run individual cases	Wrap body in t.Run(tt.name, ...)
Anonymous test cases	Hard to identify which failed	Add name field to test table
t.Parallel() + shared mutation	Data race	Isolate state per subtest
t.Parallel() + t.Setenv	Runtime panic	Use config structs instead
fmt.Println in tests	Lost in parallel output	Use t.Log/t.Logf
Manual temp dirs	Leak on failure	Use t.TempDir()

Table-Driven Test Template

func TestParse(t *testing.T) {
    tests := []struct {
        name    string
        input   string
        want    Result
        wantErr bool
    }{
        {name: "valid", input: "abc", want: Result{Value: "abc"}},
        {name: "empty", input: "", wantErr: true},
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            got, err := Parse(tt.input)
            if (err != nil) != tt.wantErr {
                t.Fatalf("Parse(%q) error = %v, wantErr %v", tt.input, err, tt.wantErr)
            }
            if !tt.wantErr && got != tt.want {
                t.Errorf("Parse(%q) = %v, want %v", tt.input, got, tt.want)
            }
        })
    }
}

Interface-Based Mocking

Go prefers small interfaces + hand-written test doubles over mocking frameworks:

type Store interface {
    Get(ctx context.Context, id string) (*Item, error)
}

type fakeStore struct {
    items map[string]*Item
}

func (f *fakeStore) Get(_ context.Context, id string) (*Item, error) {
    item, ok := f.items[id]
    if !ok {
        return nil, ErrNotFound
    }
    return item, nil
}

Use gomock/mockall only when the interface has many methods.