Testing in Go

Just list some testing way in Go.

Basically we use testing this built-in lib to testing

To start your first test with Go is an easy task.

Example(we would test the following function under directory add)

package add

func Add(x, y int) int { return x + y }
  1. create a file contains suffix _test, it would be a test file, e.g. =addtest.go=
  2. create a function in test file has prefix Test, use t *testing.T as it's parameter

    package add
    import "testing"
    func TestAdd(t *testing.T) {
     if Add(1, 2) != 3 {
         t.Errorf("Add(1, 2) should be 3 but: %d", Add(1, 2))
  3. type go test & execute it in terminal

Ok, now we got a test, if you see the error message then must something wrong about your implementation of Add

p.s. Usually we won't use go test but go test ./... because we would have a lots of package under a project, ./... would find out every sub directory(those can be a go package) & run test

We have func (*testing.T) Run(subTestName string, subTest func(t *testing.T)) this function, we can use it to create a new sub test.

func TestCarFactory(t *testing.T) {
    factory := car.NewFactory()
    t.Run("Toyota", func(t *testing.T) {
	toyota := factory.Build(car.Toyota)
	// test toyota
    t.Run("Mazda", func(t *testing.T) {
	mazda := factory.Build(car.Mazda)
	// test mazda

Basically you can see sub test means we want to reuse same context for different tests, or like me, just use it represents the test structure.

A practical problem is sometime we extract a test helper out of the test function.

For example:

func assertNoError(t *testing.T, err error) {
    if err != nil {
	t.Errorf("assert no error but: %s", err)

You will find all error say it happened at t.Errorf that line, but not the error actual happened place!

To solve this problem, you have to add t.Helper() this function call, according document:

Helper marks the calling function as a test helper function. When printing file and line information, that function will be skipped. Helper may be called simultaneously from multiple goroutines.

I recommend https://github.com/stretchr/testify for assertion, *Don't Reinvent The Wheel!*(Some thing I always violate it)

And https://github.com/gavv/httpexpect is an awesome lib for web API testing.

A nice fact is, Go also help you create benchmark easy.

Still in test file, but use Benchmark as prefix of test.

func BenchmarkAdd(b *testing.B) {
    for i := 0; i < b.N; i++ {
	Add(1, 2)

To run benchmark needs argument -bench, it would like go test -bench .


goos: darwin
goarch: amd64
pkg: test
BenchmarkAdd-4          2000000000               0.61 ns/op
ok      test    1.285s

As t.Run, you can have b.Run in benchmark.

To get the nice analysis of program, you can use go test -bench . -cpuprofile cpu.out -memprofile mem.out to generate some profiles

Then use go tool pprof -http= cpu.out to see the result on browser(if you are familiar with CLI mode, you can remove -http flag)

You can see something like:

                                            1130ms   100% |   testing.(*B).launch /usr/local/Cellar/go/1.11.2/libexec/src/testing/benchmark.go:290
         0     0%   100%     1130ms 98.26%                | testing.(*B).runN /usr/local/Cellar/go/1.11.2/libexec/src/testing/benchmark.go:141
                                            1130ms   100% |   test.BenchmarkAdd /Users/dannypsnl/code/go/src/test/add_test.go:8

At here example is too easy so nothing to show, in a real world code it would be pretty useful to know the hot point of the program.

p.s. At profile example, -bench can't be omit, because we want something run a lots of time to detect it's real performance.

If you want to get the performance under real usage, you can import pprof into program:

import (
    _ "net/http/pprof"

If your program is not a HTTP server, then you have to start one like:

go func() {
    log.Println(http.ListenAndServe("", nil))

The reason of can reference to https://stackoverflow.com/questions/20778771/what-is-the-difference-between-0-0-0-0-127-0-0-1-and-localhost

After these, you can run your program up then see your profile like go tool pprof

To get more info, you can reference:

Thanks for reading

Date: 2018-11-17 Sat 00:00

Author: Lîm Tsú-thuàn