file tests

src/io/file.js

@@ -5,7 +5,7 @@ let next_thread_id = 1;
 export default class file {
   constructor(conn, handle, remote_path) {
     this.conn = conn;
-    this.handle = handle;
+    this.handle = handle || null;
     this.remote_path = remote_path;
     this.thread_id = next_thread_id++;
   }