How to test os.exit scenarios in Go

Question

Given this code

func doomed() {   os.Exit(1) } 

How do I properly test that calling this function will result in an exit using go test? This needs to occur within a suite of tests, in other words the os.Exit() call cannot impact the other tests and should be trapped.

Answer 1

There's a presentation by Andrew Gerrand (one of the core members of the Go team) where he shows how to do it.

Given a function (in main.go)

package main  import (     "fmt"     "os" )  func Crasher() {     fmt.Println("Going down in flames!")     os.Exit(1) } 

here's how you would test it (through main_test.go):

package main  import (     "os"     "os/exec"     "testing" )  func TestCrasher(t *testing.T) {     if os.Getenv("BE_CRASHER") == "1" {         Crasher()         return     }     cmd := exec.Command(os.Args[0], "-test.run=TestCrasher")     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) } 

What the code does is invoke go test again in a separate process through exec.Command, limiting execution to the TestCrasher test (via the -test.run=TestCrasher switch). It also passes in a flag via an environment variable (BE_CRASHER=1) which the second invocation checks for and, if set, calls the system-under-test, returning immediately afterwards to prevent running into an infinite loop. Thus, we are being dropped back into our original call site and may now validate the actual exit code.

Source: Slide 23 of Andrew's presentation. The second slide contains a link to the presentation's video as well. He talks about subprocess tests at 47:09