Testing with go test

The go test command automates testing the packages named by import paths. It compiles test files, runs test functions, and reports results.

Overview

Testing is a first-class citizen in Go. The go test command provides built-in support for unit tests, benchmarks, examples, and fuzz tests.

Basic Usage

go test [build/test flags] [packages] [build/test flags & test binary flags]

# Test current package
go test

# Test with verbose output
go test -v

# Test current package (explicit)
go test .

Test Files

Test File Naming

Test files must:

End with _test.go
Be in the same package directory
Not start with _ or .

// mypackage_test.go
package mypackage

import "testing"

func TestInternal(t *testing.T) {
    // Can access unexported functions
    result := internalFunc()
    if result != expected {
        t.Errorf("got %v, want %v", result, expected)
    }
}

Test Modes

Local Directory Mode

Invoked without package arguments:

go test
go test -v

Compiles package in current directory
Runs test binary immediately
Caching is disabled
Prints summary after completion

Package List Mode

Invoked with explicit package arguments:

go test ./...
go test example.com/myapp

Compiles and tests each listed package
Results are cached
Prints ‘ok’ for passing tests
Shows full output for failures

Common Test Flags

Test Selection

-run

regexp

Run only tests matching regexp

# Run specific test
go test -run TestMyFunction

# Run tests matching pattern
go test -run "Test.*Integration"

# Run subtests
go test -run TestMyFunc/subtest_name

-skip

regexp

Skip tests matching regexp

go test -skip "TestSlow|TestExternal"

Output Control

-v

flag

Verbose output - print all test names and results

go test -v

-json

flag

Output test results as JSON

go test -json
go test -json | tee test-results.json

Test Execution

-count

Run each test n times (default: 1)

# Disable test caching
go test -count=1

# Run tests multiple times
go test -count=10

-parallel

Maximum number of tests to run in parallel (default: GOMAXPROCS)

go test -parallel 4

-timeout

duration

Timeout for entire test execution (default: 10m)

go test -timeout 30s
go test -timeout 5m

-short

flag

Run in short mode - skip long-running tests

go test -short

In test code:

if testing.Short() {
    t.Skip("skipping test in short mode")
}

-failfast

flag

Stop after first test failure

go test -failfast

Coverage Flags

-cover

flag

Enable coverage analysis

go test -cover

-coverprofile

file

Write coverage profile to file

go test -coverprofile=coverage.out

-covermode

set|count|atomic

Set coverage mode

set: boolean (was this line executed?)
count: count how many times each line executed
atomic: like count, but correct for concurrent tests

go test -covermode=count -coverprofile=coverage.out

Writing Tests

Basic Test Function

Create Test File

Create a file ending in _test.go:

// math_test.go
package math

import "testing"

Write Test Function

Test functions must start with Test and take *testing.T:

func TestAdd(t *testing.T) {
    result := Add(2, 3)
    expected := 5
    
    if result != expected {
        t.Errorf("Add(2, 3) = %d; want %d", result, expected)
    }
}

Run Tests

go test
go test -v

Table-Driven Tests

func TestAdd(t *testing.T) {
    tests := []struct {
        name     string
        a, b     int
        expected int
    }{
        {"positive numbers", 2, 3, 5},
        {"negative numbers", -2, -3, -5},
        {"mixed signs", -2, 3, 1},
        {"zeros", 0, 0, 0},
    }
    
    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            result := Add(tt.a, tt.b)
            if result != tt.expected {
                t.Errorf("Add(%d, %d) = %d; want %d", 
                    tt.a, tt.b, result, tt.expected)
            }
        })
    }
}

Run specific subtests:

# Run all Add tests
go test -run TestAdd

# Run specific subtest
go test -run TestAdd/positive

Testing Methods

t.Error / t.Errorf

Report error but continue test:

t.Error("something went wrong")
t.Errorf("got %v, want %v", result, expected)

t.Fatal / t.Fatalf

Report error and stop test immediately:

t.Fatal("critical failure")
t.Fatalf("setup failed: %v", err)

t.Log / t.Logf

Print log output (only shown with -v or on failure):

t.Log("debug information")
t.Logf("processing item %d", i)

t.Skip / t.Skipf

Skip test:

if runtime.GOOS == "windows" {
    t.Skip("skipping on Windows")
}

t.Cleanup

tmpFile, err := os.CreateTemp("", "test")
if err != nil {
    t.Fatal(err)
}
t.Cleanup(func() {
    os.Remove(tmpFile.Name())
})

Benchmarks

Writing Benchmarks

func BenchmarkAdd(b *testing.B) {
    for i := 0; i < b.N; i++ {
        Add(2, 3)
    }
}

func BenchmarkComplexOperation(b *testing.B) {
    // Setup (not timed)
    data := setupData()
    
    b.ResetTimer() // Reset timer after setup
    
    for i := 0; i < b.N; i++ {
        ComplexOperation(data)
    }
}

Running Benchmarks

# Run all benchmarks
go test -bench=.

# Run specific benchmark
go test -bench=BenchmarkAdd

# Run benchmarks matching pattern
go test -bench="Complex.*"

Examples

Writing Examples

func ExampleAdd() {
    result := Add(2, 3)
    fmt.Println(result)
    // Output: 5
}

func ExampleAdd_negative() {
    result := Add(-2, -3)
    fmt.Println(result)
    // Output: -5
}

func ExamplePerson_String() {
    p := Person{Name: "Alice", Age: 30}
    fmt.Println(p)
    // Output: Alice (30 years old)
}

Examples serve as both documentation and tests.

Code Coverage

Generate Coverage Profile

go test -coverprofile=coverage.out

View Coverage Report

# Text summary
go tool cover -func=coverage.out

# HTML visualization
go tool cover -html=coverage.out

Coverage for Multiple Packages

go test -coverprofile=coverage.out ./...
go tool cover -html=coverage.out

Coverage Options

# Specify packages to cover
go test -coverpkg=./... -coverprofile=coverage.out

# Different coverage modes
go test -covermode=set -coverprofile=coverage.out
go test -covermode=count -coverprofile=coverage.out
go test -covermode=atomic -coverprofile=coverage.out

Test Caching

Go caches successful test results to avoid unnecessary reruns.

Cacheable Flags

Tests are cached when using only these flags:

-benchtime
-cpu
-coverprofile
-failfast
-fullpath
-list
-outputdir
-parallel
-run
-short
-skip
-timeout
-v

Disabling Cache

# Idiomatic way to disable cache
go test -count=1

Advanced Testing

Setup and Teardown

func TestMain(m *testing.M) {
    // Setup before all tests
    setup()
    
    // Run tests
    code := m.Run()
    
    // Teardown after all tests
    teardown()
    
    os.Exit(code)
}

Parallel Tests

func TestParallel(t *testing.T) {
    t.Parallel() // Mark test as parallelizable
    
    // Test code here
}

func TestParallelSubtests(t *testing.T) {
    tests := []struct{
        name string
        // ...
    }{
        // test cases
    }
    
    for _, tt := range tests {
        tt := tt // Capture range variable
        t.Run(tt.name, func(t *testing.T) {
            t.Parallel()
            // Subtest code
        })
    }
}

Using testdata Directory

mypackage/
  ├── myfile.go
  ├── myfile_test.go
  └── testdata/
      ├── input.json
      └── expected.txt

func TestWithTestdata(t *testing.T) {
    data, err := os.ReadFile("testdata/input.json")
    if err != nil {
        t.Fatal(err)
    }
    // Use data in test
}

Test Compilation

Compile Test Binary

# Compile but don't run
go test -c

# Compile with custom output name
go test -c -o mytest.test

# Run compiled test binary
./mytest.test
./mytest.test -test.v -test.run TestSpecific

Binary Flags

Compiled test binaries accept -test.* flags:

./mytest.test -test.v
./mytest.test -test.run TestMyFunc
./mytest.test -test.bench=.
./mytest.test -test.cpuprofile=cpu.prof

CI/CD Integration

GitHub Actions

.github/workflows/test.yml

name: Test

on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      
      - uses: actions/setup-go@v5
        with:
          go-version: '1.21'
      
      - name: Run tests
        run: go test -v -race -coverprofile=coverage.out ./...
      
      - name: Upload coverage
        uses: codecov/codecov-action@v3
        with:
          files: ./coverage.out

Makefile

.PHONY: test
test:
	go test -v -race -coverprofile=coverage.out ./...

.PHONY: test-short
test-short:
	go test -short ./...

.PHONY: coverage
coverage: test
	go tool cover -html=coverage.out

.PHONY: bench
bench:
	go test -bench=. -benchmem ./...

Troubleshooting

Tests are cached when they shouldn't be

# Disable caching
go test -count=1

# Or clear cache
go clean -testcache

Tests timeout

# Increase timeout
go test -timeout 30m

# Check for infinite loops or deadlocks
go test -timeout 10s -v

Race detector issues

# Run with race detector
go test -race

# May need more memory
GORACE="history_size=7" go test -race

go Command

Overview of go command

Building

Building Go programs

Benchmarking

Performance testing

Get Started

Language Guide

Standard Library

Core Packages

Tools & Commands

Advanced Topics

Contributing

​Overview

​Basic Usage

​Test Files

​Test File Naming

​Test Modes

​Local Directory Mode

​Package List Mode

​Common Test Flags

​Test Selection

​Output Control

​Test Execution

​Coverage Flags

​Writing Tests

​Basic Test Function

​Table-Driven Tests

​Testing Methods

​Benchmarks

​Writing Benchmarks

​Running Benchmarks

​Examples

​Writing Examples

​Code Coverage

​Coverage Options

​Test Caching

​Cacheable Flags

​Disabling Cache

​Advanced Testing

​Setup and Teardown

​Parallel Tests

​Using testdata Directory

​Test Compilation

​Compile Test Binary

​Binary Flags

​CI/CD Integration

​GitHub Actions

​Makefile

​Troubleshooting

​See Also

go Command

Building

Benchmarking

Build docs developers (and LLMs) love

Overview

Basic Usage

Test Files

Test File Naming

Test Modes

Local Directory Mode

Package List Mode

Common Test Flags

Test Selection

Output Control

Test Execution

Coverage Flags

Writing Tests

Basic Test Function

Table-Driven Tests

Testing Methods

Benchmarks

Writing Benchmarks

Running Benchmarks

Examples

Writing Examples

Code Coverage

Coverage Options

Test Caching

Cacheable Flags

Disabling Cache

Advanced Testing

Setup and Teardown

Parallel Tests

Using testdata Directory

Test Compilation

Compile Test Binary

Binary Flags

CI/CD Integration

GitHub Actions

Makefile

Troubleshooting

See Also