.

go/xcommon/tracing/cmd/gotrace/gotrace_test.go

 package main
 
 import (
+	"bytes"
 	"go/build"
 	"io/ioutil"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strings"
+	"syscall"
 	"testing"
 
 	"lab.nexedi.com/kirr/go123/exc"
@@ -63,13 +66,15 @@ func prepareTestTree(src, dst string, mode TreePrepareMode) error {
 
 		switch mode {
 		case TreePrepareGolden:
-			// no removed files in golden tree
+			// ok files are written as is
+
+			// no removed files
 			if isRm {
 				return nil
 			}
 
 		case TreePrepareWork:
-			// no ok files initially in work tree
+			// no ok files initially
 			if isOk {
 				return nil
 			}
@@ -93,6 +98,20 @@ func xprepareTree(src, dst string, mode TreePrepareMode) {
 	exc.Raiseif(err)
 }
 
+// diffR compares two directories recursively
+func diffR(patha, pathb string) (diff string, err error) {
+	out := &bytes.Buffer{}
+	cmd := exec.Command("diff", "-urN", patha, pathb)
+	cmd.Stdout = out
+
+	err = cmd.Run()
+	if e, ok := err.(*exec.ExitError); ok && e.Sys().(syscall.WaitStatus).ExitStatus() == 1 {
+		err = nil // diff signals with 1 just a difference - problem exit code is 2
+	}
+
+	return out.String(), err
+}
+
 func TestGoTraceGen(t *testing.T) {
 	tmp, err := ioutil.TempDir("", "t-gotrace")
 	if err != nil {
@@ -124,9 +143,13 @@ func TestGoTraceGen(t *testing.T) {
 			t.Errorf("%v: %v", tpkg, err)
 		}
 
-		err := diffR(good+"/"+tpkg, work+"/"+tpkg)
+		diff, err := diffR(good+"/"+tpkg, work+"/"+tpkg)
 		if err != nil {
-			t.Errorf("%v: %v", tpkg, err)
+			t.Fatalf("%v: %v", tpkg, err)
+		}
+
+		if diff != "" {
+			t.Errorf("%v: gold & work differ:\n%s", tpkg, diff)
 		}
 	}
 }