Some nifty test helpers inspired by @mitchellh https://www.youtube.com/watch?v=yszygk1cpEc

git_test.go

package main

import (
	"os"
	"testing"
)

func TestGetSHA(t *testing.T) {
	sha, err := getSHA1()
	if err != nil {
		t.Fatal(err)
	}

	const hexDigits = 40 // sha1.Size * 2

	if len(sha) != hexDigits {
		t.Errorf("Expected SHA to be %d hex digits, was %d", hexDigits, len(sha))
	}
}

func TestGitNotInPath(t *testing.T) {
	defer changeEnv(t, "PATH", ".")()

	_, err := getSHA1()
	if err == nil || err.Error() != `exec: "git": executable file not found in $PATH` {
		t.Fatalf("Expected error %q, got %v.", "executable file not found", err)
	}
}

func TestNotGitDirectory(t *testing.T) {
	defer changeDir(t, os.TempDir())()

	_, err := getSHA1()
	if err == nil || err.Error() != "fatal: Not a git repository (or any of the parent directories): .git" {
		t.Fatalf("Expected error %q, got %v.", "Not a git repository", err)
	}
}

// changeEnv temporarily changes the environment
func changeEnv(t *testing.T, key, value string) func() {
	was := os.Getenv(key)
	fatalIfError(t, os.Setenv(key, value))
	return func() {
		fatalIfError(t, os.Setenv(key, was))
	}
}

// changeDir temporarily changes the working directory
func changeDir(t *testing.T, dir string) func() {
	wd, err := os.Getwd()
	fatalIfError(t, err)
	fatalIfError(t, os.Chdir(dir))

	return func() {
		fatalIfError(t, os.Chdir(wd))
	}
}

// fail the tests if an unexpected error occurred
func fatalIfError(t *testing.T, err error) {
	if err != nil {
		t.Fatal(err)
	}
}