Golang: Testing with init() func

Hi I am new to Go and I am writing a simple app which gets some configuration from the env variables. I do this in the init function as shown below.

type envVars struct {
	Host     string `env:"APP_HOST"`
	Username string `env:"APP_USERNAME"`
	Password string `env:"APP_PASSWORD"`
}

var envConfig envVars

func init() {
	if err := env.Parse(&envConfig); err != nil {
		log.Fatal(err)
	}
}

I wrote test to verify of the env variables are being read correctly. But the problem is that my program's init func gets called even before my test's init func. Is there any way I can do some sort of setup before my program's init func gets called.

func init() {
	os.Setenv("APP_HOST", "http://localhost:9999")
	os.Setenv("APP_USERNAME", "john")
	os.Setenv("APP_PASSWORD", "doe")
}

func TestEnvConfig(t *testing.T) {
	assert.NotNil(t, envConfig)
	assert.Equal(t, "http://localhost:9999", envConfig.Host)
}

You can use the TestMain func to control what happens before and after your tests.

For example:

func TestMain(m *testing.M) {
    // Write code here to run before tests
    
    // Run tests
    exitVal := m.Run()
    
    // Write code here to run after tests

    // Exit with exit value from tests
    os.Exit(exitVal)
}

func TestYourFunc(t *testing.T) {
    // Test code
}

You can add a Test_parse_params(t *testing.T) function before your real tests. Look like this:

type envVars struct {
    Host     string `env:"APP_HOST"`
    Username string `env:"APP_USERNAME"`
    Password string `env:"APP_PASSWORD"`
}

var envConfig envVars

//parse command params
func Test_parse_params(t *testing.T) {
    if err := env.Parse(&envConfig); err != nil {
        log.Fatal(err)
    }
}

func Test_real_test(t *testing.T) {
....
}

No, you shouldn't expect init() run in some order, (in fact it based on file loaded order, but still, you should not count on it).

The simple way is, if you want to test it, use a shell script to run you test, or something like Makefile.

Shell example:

set +e
export APP_HOST=http://localhost:9999
export APP_USERNAME=john
export APP_PASSWORD=doe
go test .
unset APP_HOST
unset APP_USERNAME
unset APP_PASSWORD

or a single line command:

APP_HOST=http://localhost:9999 APP_USERNAME=john APP_PASSWORD=doe go test .

Edit:

Other solution: move out the read env from init func.

func init(){
  envInit()
}
func envInit(){
 if err := env.Parse(&envConfig); err != nil {
        log.Fatal(err)
    }
}

Then you can call again envInit in your test to make sure it works.

Less than ideal, but this works for me.
Inside of the package that you're testing:

func init() {
    if len(os.Args) > 1 && os.Args[1][:5] == "-test" {
    	log.Println("testing")//special test setup goes goes here
        return // ...or just skip the setup entirely
    }
    //...
}