Go (GoLang) Testing

The following program prints out Hello World from the type of gopher, unless the gopher is dead.

$ go run hello.go -g 'small'
Hello World from small gopher!

# But if it's a dead gopher

$ go run hello.go -g 'dead'
2018/04/14 12:58:23 Fatal exit: ... cannot go on
exit status 1

So note above, for dead type of gopher, we want an exit status of 1.

package main

import (
	"log"
	"flag"
	"fmt"
)

var gopherType string

func init() {
	const (
		defaultGopher = "pocket"
		usage         = "the variety of gopher"
	)
	flag.StringVar(&gopherType, "gopher_type", defaultGopher, usage)
	flag.StringVar(&gopherType, "g", defaultGopher, usage+" (shorthand)")
}

func fatalExit(s string) {
	log.Fatalf("Fatal exit: %v", s)
}

func main() {

	flag.Parse()

	if gopherType == "dead" {
		fatalExit("... cannot go on")
	}

	fmt.Printf("Hello World from %v gopher!\n\n",gopherType)

}

Testing

We can use the following to test the program exit status 1, when the flag input is “dead” with the command -g “dead”.

package main

import (
	"testing"
	"os"
	"os/exec"
	"flag"
)

func TestMain(m *testing.M) {
	flag.Parse()
	os.Exit(m.Run())
}

// Very cool... see
//  https://talks.golang.org/2014/testing.slide#23
func TestFatalExit(t *testing.T) {

	// This is true on 2nd pass through this function.
	if os.Getenv("BE_CRASHER") == "1" {
		flag.Set("g", "dead")    // Set the Flag
		main()                   // Call to main
		return
	}

	cmd := exec.Command(os.Args[0], "-test.run=TestFatalExit")
	cmd.Env = append(os.Environ(), "BE_CRASHER=1")
	err := cmd.Run()
	if e, ok := err.(*exec.ExitError); ok && !e.Success() {
		return
	}
	t.Fatalf("process ran with err %v, want exit status 1", err)
}