我如何知道两台服务器何时准备接收请求？

I have two servers

router := createServer()
loginServer := createLoginServerMock()
servLogin := &http.Server{
    Addr:         ":9333",
    Handler:      loginServer,
}
testServer := &http.Server{
    Addr:         ":9444",
    Handler:      router,
}
loginServer.ListenAndServe()
testServer.ListenAndServe()

And I want to send request on both of them after they created? How can I detect that?

ListenAndServe has no feedback mechanism to let you know when the server is ready. You have to create the listener yourself and pass it to Server.Serve:

loginListener, err := net.Listen("tcp", ":9333")
if err != nil {
    // TODO: handle err
}

testListener, err := net.Listen("tcp", ":9444")
if err != nil {
    // TODO: handle err
}

// You may already start sending requests now. They will just wait until
// the servers call Accept on their respective listener (i.e. shortly after
// Serve is called).

servLogin := &http.Server{Handler: loginServer}
testServer := &http.Server{Handler: router}

go func() { log.Fatal(servLogin.Serve(loginListener)) }()
go func() { log.Fatal(testServer.Serve(testListener)) }()

ListenAndServe() will return an error when create server failed. Just handle it to known server start success or not. I can see your coding will only start login server while test server be hanging. Let's try

go func() {
  log.Fatal(loginServer.ListenAndServe())
}
log.Fatal(testServer.ListenAndServe())

The program will wait at 1st ListenAndServe() until any error occurred. Because the ListenAndServe() method runs forever. So your second server will never started until the execution goes to the next ListenAndServe(). So use go in front of the 1st server's statement:

router := createServer()
loginServer := createLoginServerMock()
go func() {
    if err := http.ListenAndServe(":9333", loginServer); err != nil {
        log.Fatal("login server err: ", err)
    }
}()
if err := http.ListenAndServe(":9444", router); err != nil {
    log.Fatal("test server err: ", err)
}

Then access your loginServer at http://localhost:9333 and testServer at http://localhost:9444.