cmd/go/internal/work: more TestRespectSetgidDir fixes

Hopefully the last refactoring of TestRespectGroupSticky:
* Properly tested (+simplified) FreeBSD fix
* Tested on Darwin (10.12.4)
* Rename to TestRespectSetgidDir (I believe this is the accepted
  terminology)

Fixes golang/go#19596.

Change-Id: I8d689ac3e245846cb3f1338ea13e35be512ccb9c
Reviewed-on: https://go-review.googlesource.com/41430Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>

src/cmd/go/internal/work/build_test.go

@@ -171,12 +171,12 @@ func pkgImportPath(pkgpath string) *load.Package {
 }
 
 // When installing packages, the installed package directory should
-// respect the group sticky bit and group name of the destination
+// respect the SetGID bit and group name of the destination
 // directory.
 // See https://golang.org/issue/18878.
-func TestRespectGroupSticky(t *testing.T) {
+func TestRespectSetgidDir(t *testing.T) {
 	if runtime.GOOS == "nacl" {
-		t.Skip("can't set group sticky bit with chmod on nacl")
+		t.Skip("can't set SetGID bit with chmod on nacl")
 	}
 
 	var b Builder
@@ -189,19 +189,21 @@ func TestRespectGroupSticky(t *testing.T) {
 		return cmdBuf.WriteString(fmt.Sprint(a...))
 	}
 
-	stickydir, err := ioutil.TempDir("", "GroupSticky")
+	setgiddir, err := ioutil.TempDir("", "SetGroupID")
 	if err != nil {
 		t.Fatal(err)
 	}
-	defer os.RemoveAll(stickydir)
+	defer os.RemoveAll(setgiddir)
 
-	testdir, err := ioutil.TempDir(stickydir, "testdir")
-	if err != nil {
-		t.Fatal(err)
+	if runtime.GOOS == "freebsd" {
+		err = os.Chown(setgiddir, os.Getuid(), os.Getgid())
+		if err != nil {
+			t.Fatal(err)
+		}
 	}
 
-	// Change testdir's permissions to include group sticky bit.
-	if err := os.Chmod(testdir, 0755|os.ModeSetgid); err != nil {
+	// Change setgiddir's permissions to include the SetGID bit.
+	if err := os.Chmod(setgiddir, 0755|os.ModeSetgid); err != nil {
 		t.Fatal(err)
 	}
 
@@ -212,14 +214,14 @@ func TestRespectGroupSticky(t *testing.T) {
 	defer os.Remove(pkgfile.Name())
 	defer pkgfile.Close()
 
-	stickyFile := filepath.Join(testdir, "sticky")
-	if err := b.moveOrCopyFile(nil, stickyFile, pkgfile.Name(), 0666, true); err != nil {
+	dirGIDFile := filepath.Join(setgiddir, "setgid")
+	if err := b.moveOrCopyFile(nil, dirGIDFile, pkgfile.Name(), 0666, true); err != nil {
 		t.Fatalf("moveOrCopyFile: %v", err)
 	}
 
 	got := strings.TrimSpace(cmdBuf.String())
-	want := b.fmtcmd("", "cp %s %s", pkgfile.Name(), stickyFile)
+	want := b.fmtcmd("", "cp %s %s", pkgfile.Name(), dirGIDFile)
 	if got != want {
-		t.Fatalf("moveOrCopyFile(%q, %q): want %q, got %q", stickyFile, pkgfile.Name(), want, got)
+		t.Fatalf("moveOrCopyFile(%q, %q): want %q, got %q", dirGIDFile, pkgfile.Name(), want, got)
 	}
 }