Use random port in test webserver

test/test.js

@@ -60,7 +60,7 @@ function parseOptions() {
     .example('$0 --b=firefox -t=issue5567 -t=issue5909',
       'Run the reftest identified by issue5567 and issue5909 in Firefox.')
     .describe('port', 'The port the HTTP server should listen on.')
-    .default('port', 8000)
+    .default('port', 0)
     .describe('unitTest', 'Run the unit tests.')
     .describe('fontTest', 'Run the font tests.')
     .describe('noDownload', 'Skips test PDFs downloading.')

test/webserver.js

@@ -44,7 +44,7 @@ var defaultMimeType = 'application/octet-stream';
 function WebServer() {
   this.root = '.';
   this.host = 'localhost';
-  this.port = 8000;
+  this.port = 0;
   this.server = null;
   this.verbose = false;
   this.cacheExpirationTime = 0;
@@ -56,6 +56,7 @@ function WebServer() {
 }
 WebServer.prototype = {
   start: function (callback) {
+    this._ensureNonZeroPort();
     this.server = http.createServer(this._handler.bind(this));
     this.server.listen(this.port, this.host, callback);
     console.log(
@@ -65,6 +66,19 @@ WebServer.prototype = {
     this.server.close(callback);
     this.server = null;
   },
+  _ensureNonZeroPort: function () {
+    if (!this.port) {
+      // If port is 0, a random port will be chosen instead. Do not set a host
+      // name to make sure that the port is synchronously set by .listen().
+      var server = http.createServer().listen(0);
+      var address = server.address();
+      // .address().port being available synchronously is merely an
+      // implementation detail. So we are defensive here and fall back to some
+      // fixed port when the address is not available yet.
+      this.port = address ? address.port : 8000;
+      server.close();
+    }
+  },
   _handler: function (req, res) {
     var url = req.url;
     var urlParts = /([^?]*)((?:\?(.*))?)/.exec(url);