diff --git a/godoc/dirtrees_test.go b/godoc/dirtrees_test.go
new file mode 100644
index 0000000..c8e8827
--- /dev/null
+++ b/godoc/dirtrees_test.go
@@ -0,0 +1,40 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package godoc
+
+import (
+	"runtime"
+	"sort"
+	"testing"
+
+	"golang.org/x/tools/godoc/vfs"
+	"golang.org/x/tools/godoc/vfs/gatefs"
+)
+
+func TestNewDirTree(t *testing.T) {
+	fsGate := make(chan bool, 20)
+	rootfs := gatefs.New(vfs.OS(runtime.GOROOT()), fsGate)
+	fs := vfs.NameSpace{}
+	fs.Bind("/", rootfs, "/", vfs.BindReplace)
+
+	c := NewCorpus(fs)
+	// 3 levels deep is enough for testing
+	dir := c.newDirectory("/", 3)
+
+	processDir(t, dir)
+}
+
+func processDir(t *testing.T, dir *Directory) {
+	var list []string
+	for _, d := range dir.Dirs {
+		list = append(list, d.Name)
+		// recursively process the lower level
+		processDir(t, d)
+	}
+
+	if sort.StringsAreSorted(list) == false {
+		t.Errorf("list: %v is not sorted\n", list)
+	}
+}