fix listening handler

lib/local-web-server.js

@@ -164,16 +164,17 @@ class LocalWebServer {
 
     const tableLayout = require('table-layout')
 
-    server
-      .listen(options.port)
-      .on('listening', function () {
-        if (options.testMode) return 
+    server.listen(options.port)
+    if (onListening) server.on('listening', onListening)
+    if (!options.testMode) {
+      server.on('listening', function () {
         const ipList = getIPList()
           .map(iface => `[underline]{${server.isHttps ? 'https' : 'http'}://${iface.address}:${options.port}}`)
           .join(', ')
         console.error(ansi.format('Serving at', 'bold'), ansi.format(ipList))
       })
-      .on('listening', onListening)
+    }
+
     return server
   }