cmd/go: fix TestExecutableGOROOT if GOROOT is a symlink

Fixes #20365.

Change-Id: If1a4866193cff3bc836d8bbf18b6a1f5deb9808d
Reviewed-on: https://go-review.googlesource.com/43550
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Alessandro Arzilli <alessandro.arzilli@gmail.com>

src/cmd/go/go_test.go

@@ -3969,9 +3969,13 @@ func TestExecutableGOROOT(t *testing.T) {
 		out, err := cmd.CombinedOutput()
 		if err != nil {
 			t.Fatalf("copied go tool failed %v: %s", err, out)
-			return ""
 		}
-		return strings.TrimSpace(string(out))
+		root := strings.TrimSpace(string(out))
+		resolved, err := filepath.EvalSymlinks(root)
+		if err != nil {
+			t.Fatalf("EvalSymlinks(%q) failed: %v", root, err)
+		}
+		return resolved
 	}
 
 	// Filenames are case insensitive on Windows.
@@ -3995,7 +3999,11 @@ func TestExecutableGOROOT(t *testing.T) {
 
 	// Now the executable's path looks like a GOROOT.
 	tg.tempDir("newgoroot/pkg/tool")
-	if got, want := goroot(newGoTool), tg.path("newgoroot"); !equal(got, want) {
+	resolvedNewGOROOT, err := filepath.EvalSymlinks(tg.path("newgoroot"))
+	if err != nil {
+		t.Fatalf("could not eval newgoroot symlinks: %v", err)
+	}
+	if got, want := goroot(newGoTool), resolvedNewGOROOT; !equal(got, want) {
 		t.Fatalf("%s env GOROOT = %q with pkg/tool, want %q", newGoTool, got, want)
 	}
 
@@ -4005,11 +4013,6 @@ func TestExecutableGOROOT(t *testing.T) {
 	symGoTool := tg.path("notgoroot/bin/go" + exeSuffix)
 	tg.must(os.Symlink(newGoTool, symGoTool))
 
-	resolvedNewGOROOT, err := filepath.EvalSymlinks(tg.path("newgoroot"))
-	if err != nil {
-		t.Fatalf("could not eval newgoroot symlinks: %v", err)
-	}
-
 	if got, want := goroot(symGoTool), resolvedNewGOROOT; !equal(got, want) {
 		t.Fatalf("%s env GOROOT = %q, want %q", symGoTool, got, want)
 	}