Persona: You are a Go engineer who treats tests as executable specifications. You write tests to constrain behavior, not to hit coverage targets.

Thinking mode: Use

ultrathink

for test strategy design and failure analysis. Shallow reasoning misses edge cases and produces brittle tests that pass today but break tomorrow.

Modes:

Write mode — generating new tests for existing or new code. Work sequentially through the code under test; use
```
gotests
```
to scaffold table-driven tests, then enrich with edge cases and error paths.
Review mode — reviewing a PR's test changes. Focus on the diff: check coverage of new behaviour, assertion quality, table-driven structure, and absence of flakiness patterns. Sequential.
Audit mode — auditing an existing test suite for gaps, flakiness, or bad patterns (order-dependent tests, missing
```
t.Parallel()
```
, implementation-detail coupling). Launch up to 3 parallel sub-agents split by concern: (1) unit test quality and coverage gaps, (2) integration test isolation and build tags, (3) goroutine leaks and race conditions.
Debug mode — a test is failing or flaky. Work sequentially: reproduce reliably, isolate the failing assertion, trace the root cause in production code or test setup.

Community default. A company skill that explicitly supersedes
samber/cc-skills-golang@golang-testing
skill takes precedence.

Go Testing Best Practices

This skill guides the creation of production-ready tests for Go applications. Follow these principles to write maintainable, fast, and reliable tests.

Best Practices Summary

Table-driven tests MUST use named subtests -- every test case needs a
```
name
```
field passed to
```
t.Run
```
Integration tests MUST use build tags (
```
//go:build integration
```
) to separate from unit tests
Tests MUST NOT depend on execution order -- each test MUST be independently runnable
Independent tests SHOULD use
```
t.Parallel()
```
when possible
NEVER test implementation details -- test observable behavior and public API contracts
Packages with goroutines SHOULD use
```
goleak.VerifyTestMain
```
in
```
TestMain
```
to detect goroutine leaks
Use testify as helpers, not a replacement for standard library
Mock interfaces, not concrete types
Keep unit tests fast (< 1ms), use build tags for integration tests
Run tests with race detection in CI
Include examples as executable documentation

Test Structure and Organization

File Conventions

// package_test.go - tests in same package (white-box, access unexported)
package mypackage

// mypackage_test.go - tests in test package (black-box, public API only)
package mypackage_test

Naming Conventions

func TestAdd(t *testing.T) { ... }              // function test
func TestMyStruct_MyMethod(t *testing.T) { ... } // method test
func BenchmarkAdd(b *testing.B) { ... }          // benchmark
func ExampleAdd() { ... }                        // example

Table-Driven Tests

Table-driven tests are the idiomatic Go way to test multiple scenarios. Always name each test case.

func TestCalculatePrice(t *testing.T) {
    tests := []struct {
        name     string
        quantity int
        unitPrice float64
        expected  float64
    }{
        {
            name:      "single item",
            quantity:  1,
            unitPrice: 10.0,
            expected:  10.0,
        },
        {
            name:      "bulk discount - 100 items",
            quantity:  100,
            unitPrice: 10.0,
            expected:  900.0, // 10% discount
        },
        {
            name:      "zero quantity",
            quantity:  0,
            unitPrice: 10.0,
            expected:  0.0,
        },
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            got := CalculatePrice(tt.quantity, tt.unitPrice)
            if got != tt.expected {
                t.Errorf("CalculatePrice(%d, %.2f) = %.2f, want %.2f",
                    tt.quantity, tt.unitPrice, got, tt.expected)
            }
        })
    }
}

Unit Tests

Unit tests should be fast (< 1ms), isolated (no external dependencies), and deterministic.

Testing HTTP Handlers

Use

httptest

for handler tests with table-driven patterns. See HTTP Testing for examples with request/response bodies, query parameters, headers, and status code assertions.

Goroutine Leak Detection with goleak

Use

go.uber.org/goleak

to detect leaking goroutines, especially for concurrent code:

import (
    "testing"
    "go.uber.org/goleak"
)

func TestMain(m *testing.M) {
    goleak.VerifyTestMain(m)
}

To exclude specific goroutine stacks (for known leaks or library goroutines):

func TestMain(m *testing.M) {
    goleak.VerifyTestMain(m,
        goleak.IgnoreCurrent(),
    )
}

Or per-test:

func TestWorkerPool(t *testing.T) {
    defer goleak.VerifyNone(t)
    // ... test code ...
}

testing/synctest for Deterministic Goroutine Testing

Experimental:
testing/synctest
is not yet covered by Go's compatibility guarantee. Its API may change in future releases. For stable alternatives, use
clockwork
(see Mocking).

testing/synctest

(Go 1.24+) provides deterministic time for concurrent code testing. Time advances only when all goroutines are blocked, making ordering predictable.

When to use

synctest

instead of real time:

Testing concurrent code with time-based operations (time.Sleep, time.After, time.Ticker)
When race conditions need to be reproducible
When tests are flaky due to timing issues

import (
    "testing"
    "time"
    "testing/synctest"
    "github.com/stretchr/testify/assert"
)

func TestChannelTimeout(t *testing.T) {
    synctest.Run(func(t *testing.T) {
        is := assert.New(t)

        ch := make(chan int, 1)
        go func() {
            time.Sleep(50 * time.Millisecond)
            ch <- 42
        }()

        select {
        case v := <-ch:
            is.Equal(42, v)
        case <-time.After(100 * time.Millisecond):
            t.Fatal("timeout occurred")
        }
    })
}

Key differences in

synctest

```
time.Sleep
```
advances synthetic time instantly when the goroutine blocks
```
time.After
```
fires when synthetic time reaches the duration
All goroutines run to blocking points before time advances
Test execution is deterministic and repeatable

Test Timeouts

For tests that may hang, use a timeout helper that panics with caller location. See Helpers.

Benchmarks

→ See

samber/cc-skills-golang@golang-benchmark

skill for advanced benchmarking:

b.Loop()

(Go 1.24+),

benchstat

, profiling from benchmarks, and CI regression detection.

Write benchmarks to measure performance and detect regressions:

func BenchmarkStringConcatenation(b *testing.B) {
    b.Run("plus-operator", func(b *testing.B) {
        for i := 0; i < b.N; i++ {
            result := "a" + "b" + "c"
            _ = result
        }
    })

    b.Run("strings.Builder", func(b *testing.B) {
        for i := 0; i < b.N; i++ {
            var builder strings.Builder
            builder.WriteString("a")
            builder.WriteString("b")
            builder.WriteString("c")
            _ = builder.String()
        }
    })
}

Benchmarks with different input sizes:

func BenchmarkFibonacci(b *testing.B) {
    sizes := []int{10, 20, 30}
    for _, size := range sizes {
        b.Run(fmt.Sprintf("n=%d", size), func(b *testing.B) {
            b.ReportAllocs()
            for i := 0; i < b.N; i++ {
                Fibonacci(size)
            }
        })
    }
}

Parallel Tests

Use

t.Parallel()

to run tests concurrently:

func TestParallelOperations(t *testing.T) {
    tests := []struct {
        name string
        data []byte
    }{
        {"small data", make([]byte, 1024)},
        {"medium data", make([]byte, 1024*1024)},
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            t.Parallel()
            is := assert.New(t)

            result := Process(tt.data)
            is.NotNil(result)
        })
    }
}

Fuzzing

Use fuzzing to find edge cases and bugs:

func FuzzReverse(f *testing.F) {
    f.Add("hello")
    f.Add("")
    f.Add("a")

    f.Fuzz(func(t *testing.T, input string) {
        reversed := Reverse(input)
        doubleReversed := Reverse(reversed)
        if input != doubleReversed {
            t.Errorf("Reverse(Reverse(%q)) = %q, want %q", input, doubleReversed, input)
        }
    })
}

Examples as Documentation

Examples are executable documentation verified by

go test

func ExampleCalculatePrice() {
    price := CalculatePrice(100, 10.0)
    fmt.Printf("Price: %.2f\n", price)
    // Output: Price: 900.00
}

func ExampleCalculatePrice_singleItem() {
    price := CalculatePrice(1, 25.50)
    fmt.Printf("Price: %.2f\n", price)
    // Output: Price: 25.50
}

Code Coverage

bash

# Generate coverage file
go test -coverprofile=coverage.out ./...

# View coverage in HTML
go tool cover -html=coverage.out

# Coverage by function
go tool cover -func=coverage.out

# Total coverage percentage
go tool cover -func=coverage.out | grep total

Integration Tests

Use build tags to separate integration tests from unit tests:

//go:build integration

package mypackage

func TestDatabaseIntegration(t *testing.T) {
    db, err := sql.Open("postgres", os.Getenv("DATABASE_URL"))
    if err != nil {
        t.Fatal(err)
    }
    defer db.Close()

    // Test real database operations
}

Run integration tests separately:

bash

go test -tags=integration ./...

For Docker Compose fixtures, SQL schemas, and integration test suites, see Integration Testing.

Mocking

Mock interfaces, not concrete types. Define interfaces where consumed, then create mock implementations.

For mock patterns, test fixtures, and time mocking, see Mocking.

Enforce with Linters

Many test best practices are enforced automatically by linters:

thelper

paralleltest

testifylint

. See the

samber/cc-skills-golang@golang-linter

skill for configuration and usage.

Cross-References

-> See
```
samber/cc-skills-golang@golang-stretchr-testify
```
skill for detailed testify API (assert, require, mock, suite)
-> See
```
samber/cc-skills-golang@golang-database
```
skill (testing.md) for database integration test patterns
-> See
```
samber/cc-skills-golang@golang-concurrency
```
skill for goroutine leak detection with goleak
-> See
```
samber/cc-skills-golang@golang-continuous-integration
```
skill for CI test configuration and GitHub Actions workflows
-> See
```
samber/cc-skills-golang@golang-linter
```
skill for testifylint and paralleltest configuration

Quick Reference

bash

go test ./...                          # all tests
go test -run TestName ./...            # specific test by exact name
go test -run TestName/subtest ./...    # subtests within a test
go test -run 'Test(Add|Sub)' ./...     # multiple tests (regexp OR)
go test -run 'Test[A-Z]' ./...         # tests starting with capital letter
go test -run 'TestUser.*' ./...        # tests matching prefix
go test -run '.*Validation.*' ./...    # tests containing substring
go test -run TestName/. ./...          # all subtests of TestName
go test -run '/(unit|integration)' ./... # filter by subtest name
go test -race ./...                    # race detection
go test -cover ./...                   # coverage summary
go test -bench=. -benchmem ./...       # benchmarks
go test -fuzz=FuzzName ./...           # fuzzing
go test -tags=integration ./...        # integration tests

golang-testing

NPX Install

Tags

SKILL.md Content

Go Testing Best Practices

Best Practices Summary

Test Structure and Organization

File Conventions

Naming Conventions

Table-Driven Tests

Unit Tests

Testing HTTP Handlers

Goroutine Leak Detection with goleak

testing/synctest for Deterministic Goroutine Testing

Test Timeouts

Benchmarks

Parallel Tests

Fuzzing

Examples as Documentation

Code Coverage

Integration Tests

Mocking

Enforce with Linters

Cross-References

Quick Reference