How to Test `os.Exit` Scenarios in Go Without Crashing Your Test Suite?

Testing os.exit Scenarios in Go

In Go, the os.Exit function halts the program execution and exits the operating system. But how do we test scenarios involving os.Exit within a test suite without affecting other tests?

Consider the following code:

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

To test that calling doomed results in an exit, we can't simply call it within the test, as it would terminate the test runner as well. Instead, let's explore the approach demonstrated by Andrew Gerrand.

Gerrand's method involves running the test in a separate process. This allows us to encapsulate the os.Exit call within the separate process, ensuring it doesn't impact the main test runner.

Here's how it works:

// 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)
}

This test invokes go test again in a separate process, targeting only the TestCrasher test. It sets an environment variable (BE_CRASHER) that the subprocess checks for. If set, the subprocess calls Crasher and exits immediately to avoid infinite recursion.

Meanwhile, the original test process can then validate the exit code of the subprocess, ensuring that it terminated as expected.

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