testutils/diff.go

// Package testutils provides some useful helpers for buildozer/buildifer tests.
package testutils

import (
	"io/ioutil"
	"os"
	"os/exec"
	"testing"
)

// Diff returns the output of running diff on b1 and b2.
func Diff(b1, b2 []byte) ([]byte, error) {
	f1, err := ioutil.TempFile("", "testdiff")
	if err != nil {
		return nil, err
	}
	defer os.Remove(f1.Name())
	defer f1.Close()

	f2, err := ioutil.TempFile("", "testdiff")
	if err != nil {
		return nil, err
	}
	defer os.Remove(f2.Name())
	defer f2.Close()

	f1.Write(b1)
	f2.Write(b2)

	data, err := exec.Command("diff", "-u", f1.Name(), f2.Name()).CombinedOutput()
	if len(data) > 0 {
		// diff exits with a non-zero status when the files don't match.
		// Ignore that failure as long as we get output.
		err = nil
	}
	return data, err
}

// Tdiff logs the Diff output to t.Error.
func Tdiff(t *testing.T, a, b []byte) {
	data, err := Diff(a, b)
	if err != nil {
		t.Error(err)
		return
	}
	t.Error(string(data))
}