extract koa-mock-response and lws stack

lib/local-web-server.js

@@ -18,15 +18,22 @@ const tool = new CommandLineTool()
  * @alias module:local-web-server
  * @extends module:middleware-stack
  */
-class LocalWebServer extends DefaultStack {
+class LocalWebServer {
+  constructor (stack) {
+    this.stack = stack || new DefaultStack()
+    this.stack.addAll()
+  }
   _init (options) {
-    this.options = this.options || Object.assign(options || {}, collectUserOptions(this.getOptionDefinitions()))
+    this.options = this.options || Object.assign(options || {}, collectUserOptions(this.stack.getOptionDefinitions()))
+  }
+  addStack (stack) {
+    this.stack = stack
   }
   getApplication (options) {
     this._init(options)
     const Koa = require('koa')
     const app = new Koa()
-    app.use(this.compose(this.options))
+    app.use(this.stack.compose(this.options))
     return app
   }