call callback once on listen error

test/app.listen.js

@@ -1,6 +1,7 @@
 'use strict'
 
 var express = require('../')
+var assert = require('assert')
 
 describe('app.listen()', function(){
   it('should wrap with an HTTP server', function(done){
@@ -10,4 +11,17 @@ describe('app.listen()', function(){
       server.close(done)
     });
   })
+  it('should callback on HTTP server errors', function (done) {
+    var app1 = express()
+    var app2 = express()
+
+    var server1 = app1.listen(0, function (err) {
+      assert(!err)
+      app2.listen(server1.address().port, function (err) {
+        assert(err.code === 'EADDRINUSE')
+        server1.close()
+        done()
+      })
+    })
+  })
 })