I dont how to use “path” in app.use(). It gives me a result that I was not expected

I am new in express.js and I want to know how to use “path” in app.use() excatly. When I try the code which is following, I get a result but I am so confusing. Can you explain why the result is like that. Thank you so much.

My code is following:

const express = require('express');
const router = express.Router()
const app  = express();
const port = 3000;

app.listen(port, ()=>{
    console.log("Running");
})

app.use("/test",router)
// app.use()


router.get("/test",(req,res,next)=>{
    console.log("test 1");
    console.log(req.originalUrl);
    next()
})


router.get("/",(req,res,next)=>{
    console.log("first /");
    console.log(req.originalUrl);
    next()
})
router.get("/test",(req,res,next)=>{
    console.log("test 2");
    console.log(req.originalUrl);
    next()
})

router.get("/",(req,res,next)=>{
    console.log("second /");
    console.log(req.originalUrl);
    next()
})

And, I did test in “http://localhost:3000/test” but the result is not as I expected. Console output is :

first /
/test
second /
/test

But I was expected that result will be

test 1
/test
test 2
/test

Why is it like that? Could you explain to me? Thank you so much.