HTTP SERVER test not working properly about stream-adventure HOT 4 CLOSED

var through = require('through');
var http = require('http');
var tr = through(function(buf) {
    this.queue(buf.toString().toUpperCase());
}, function() {
    this.queue(null);
});

http.createServer(function(req, res) {
    if(req.method === "POST") {
        req.pipe(tr).pipe(res);
        res.end() // <======= causes test to pass
    }
}).listen(process.argv[2]);