开玩笑：无法读取未定义的属性（读取“0”）

Question

I'm newbie with jest and I have made a test to check several calls to datababase from an url.

I run the test with this command:

npx jest --watchAll file.test.js

And everything works fine. But, If I modify a comma, for example, the test is running again and I've got errors. I haven't any "OK" from the api and I've got this error too:

TypeError: Cannot read properties of undefined (reading '0')

When I try to check what I have received with what I have expected, like we can see in this line:

expect(1).toBe(result.data[0].id);

If I stop the test and run again with: npx jest --watchAl file.test.js everything works fine.

What happend? Why Have I got these errors when the test is running for twice?

The code of my test is:

import config from "../config";
import {getData} from "../com/functions";

describe("Test several connections with Postgress making a request via POST", () => {
    describe("Test read data from database", () => {
        test("Test 1: Read data from tbl001_users", async () => {
            let data = {
                "query": 1,
                "origin": "Mapping-Service"
            };
    
            let result = await getData(`${config.backend.protocol}://${config.backend.domain}:${config.backend.port}/api/youmalou`, data);
            console.log(result);
            expect(1).toBe(result.data[0].id);
            expect("OVT").toBe(result.data[0].code);
            expect(2).toBe(result.data[1].id);
            expect("TTHOT").toBe(result.data[1].code);
        });
        test("Test 2: Read data from tbl001_users", async () => {
            let data = {
                "query": 1,
                "origin": "Mapping-Service"
            };
    
            let result = await getData(`${config.backend.protocol}://${config.backend.domain}:${config.backend.port}/api/youmalou`, data);
            expect(1).toBe(result.data[0].id);
            expect("OVT").toBe(result.data[0].code);
            expect(2).toBe(result.data[1].id);
            expect("TTHOT").toBe(result.data[1].code);
        });
        test("Test 3: Read data from tbl001_users", async () => {
            let data = {
                "query": 1,
                "origin": "Mapping-Service"
            };
    
            let result = await getData(`${config.backend.protocol}://${config.backend.domain}:${config.backend.port}/api/youmalou`, data);
            expect(1).toBe(result.data[0].id);
            expect("OVT").toBe(result.data[0].code);
            expect(2).toBe(result.data[1].id);
            expect("TTHOT").toBe(result.data[1].code);
        });
        test("Test 4: Read data from tbl002_suppliers", async () => {
            let data = {
                "query": 2,
                "params": ["OVT"],
                "origin": "Mapping-Service"
            };
    
            let result = await getData(`${config.backend.protocol}://${config.backend.domain}:${config.backend.port}/api/youmalou`, data);
            expect("OK").toBe(result.result);
            expect(1).toBe(result.data.length);
        });
        test("Test 5: Read data from tbl002_suppliers", async () => {
            let data = {
                "query": 2,
                "params": ["OVT"],
                "origin": "Mapping-Service"
            };
    
            let result = await getData(`${config.backend.protocol}://${config.backend.domain}:${config.backend.port}/api/youmalou`, data);
            expect("OK").toBe(result.result);
            expect(1).toBe(result.data.length);
        });
        test("Test 6: Read data from tbl002_suppliers", async () => {
            let data = {
                "query": 2,
                "params": ["OVT"],
                "origin": "Mapping-Service"
            };
    
            let result = await getData(`${config.backend.protocol}://${config.backend.domain}:${config.backend.port}/api/youmalou`, data);
            expect("OK").toBe(result.result);
            expect(1).toBe(result.data.length);
        });
    });
});

The file where I dispatch the requests has this code:

import express from "express";
import {getData} from "../com/functions";
import config from "../config";
import cors from "cors";
import {YoumalouDDBB} from "../database/Youmalou/youmalou_ddbb";


const router = express.Router();

const ddbb = new YoumalouDDBB();
async function start(){
    await ddbb.connect();
}

start();

let url = null;
let urls = null;

if ((config.node_env === "test") || (config.node_env === "development") ||  (config.node_env === "production")){
    url = `${config.frontend.protocol}://${config.frontend.domain}:${config.frontend.port}`;
    urls = `${config.frontend.protocols}://${config.frontend.domain}:${config.frontend.port}`;
}

const corsOptions = {
    origin: [url, urls],
    optionSuccessStatus: 200,
    methods: ["POST", "OPTIONS"],
};

if ((config.node_env === "test") || (config.node_env === "development") || (config.node_env === "production")){
    router.all("*", cors(corsOptions));
}

router.post("/api/youmalou", async(req, res)=> {
    let result = null;
    

    if (typeof(req.body.query) === "number"){
        console.log(req.body);
        result = await ddbb.getDataFromDDBB(req.body.query, req.body.params);
    }

    res.json(result.data);
});

module.exports.Router = router;

Answer 1

I have found the problem.,. I have installed nodemon module too. So, each time I modify my code the server is restarted.

What happend? When I re running my test the server is not up at 100% and for this reason I've got an error in my requests.

The code is correct and everything works fine when the server is up previously.