testing/fstest: MapFS: set perm 0555 on synthetized dirs

As MapFS ignores filemodes and always grant read and traverse access on
directories, let's make synthetized directory entries to expose filemode
0555 instead of 0000.
Fixes #63468.

Change-Id: I5d64a6bf2f2ac6082ca5dde55b3062669fb50b8d
Reviewed-on: https://go-review.googlesource.com/c/go/+/534075
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/testing/fstest/mapfs.go

@@ -98,14 +98,14 @@ func (fsys MapFS) Open(name string) (fs.File, error) {
 		delete(need, fi.name)
 	}
 	for name := range need {
-		list = append(list, mapFileInfo{name, &MapFile{Mode: fs.ModeDir}})
+		list = append(list, mapFileInfo{name, &MapFile{Mode: fs.ModeDir | 0555}})
 	}
 	sort.Slice(list, func(i, j int) bool {
 		return list[i].name < list[j].name
 	})
 
 	if file == nil {
-		file = &MapFile{Mode: fs.ModeDir}
+		file = &MapFile{Mode: fs.ModeDir | 0555}
 	}
 	return &mapDir{name, mapFileInfo{elem, file}, list, 0}, nil
 }

src/testing/fstest/mapfs_test.go

@@ -16,7 +16,7 @@ func TestMapFS(t *testing.T) {
 		"hello":             {Data: []byte("hello, world\n")},
 		"fortune/k/ken.txt": {Data: []byte("If a program is too slow, it must have a loop.\n")},
 	}
-	if err := TestFS(m, "hello", "fortune/k/ken.txt"); err != nil {
+	if err := TestFS(m, "hello", "fortune", "fortune/k", "fortune/k/ken.txt"); err != nil {
 		t.Fatal(err)
 	}
 }
@@ -37,7 +37,7 @@ func TestMapFSChmodDot(t *testing.T) {
 	})
 	want := `
 .: drwxrwxrwx
-a: d---------
+a: dr-xr-xr-x
 a/b.txt: -rw-rw-rw-
 `[1:]
 	got := buf.String()