This is probably a reproducer for the issue eclipse-vertx/vert.x#1244
To "confuse" the connection pool, a fake server handles one request with Connection: keep-alive and the 2nd with Connection: close. If the connection close is not handled correctly a 3rd request on the connection will fail.
When running a few requests, not all finish, the test currently uses 15 requests (with a pool size of 5) and only 12 finish.