Jest Testing - Javascript XMLHttpRequest to read local file

[ccoding0]

I am new with Jest and I need to test a node.js, express application with Jest and I would really appreciate your help with this:

My app.js file save data into a JSON file that will be used in task10.js

My task10.js file reads the local JSON file sending a XMLHttpRequest() then uses the data received through the whole file. (I have tried a fetch method in task10.js and get an error fetch is not defined, tried fs read and get an error: required is not defined)and still can’t get around it. The elements return values of undefined.

How would I be able to get the exported elements from task10.js and test them in Jest after by having the following:

TASK10.JS

'use strict';

const readTextFile= function(file, callback) {
    var rawFile = new XMLHttpRequest();
    rawFile.overrideMimeType("colors1/json");
    rawFile.open("GET", file, true);
    rawFile.onreadystatechange = function() {
        if (rawFile.readyState === 4 && rawFile.status == "200") {
            callback(rawFile.responseText);
        }
    }
    rawFile.send(null);
}
//usage:
readTextFile("public/colors1.json", function(text){
    var data = JSON.parse(text);

let colors = [
      data.red,
      data.blue,
      data.green,
      data.yellow,
      data.orange,
      data.pink,
    ];

let maxRounds= 6;
 module.exports= {colors,maxRounds};  

});

TASK10.TEST.JS

  test('js file exports', () => {

let {colors,maxRounds} = require('../task10');

//examples - I will have to run different tests
 expect(typeof colors).not.toBe('undefined');

 expect(typeof maxRounds).not.toBe('undefined');
});
});

APP.JS

//function that creates file, write colors json elems on it and close file
function saveToFile(data, outFile) {
  var writeFile;
  try {
    //test a block of code for errors.
    writeFile = fs.openSync(outFile, "w");
    fs.writeSync(writeFile, data);
    fs.close(writeFile);
      console.log('saved')

  } catch (err) {
    // handle the error.
    console.log(
      "\n[" + "] Error: Unable to save " + outFile + "\n" + err + "\n"
    );
  }
}
//stringify data convert data to JSON string
let data = JSON.stringify(colors);

app.get("/task10", function (req, res) {
  //invoke function to handle file colors1.json
  saveToFile(data, "colors1.json");
  //write file that we will read via our task 10.js
  res.render("task10");
});

THANKS A LOT IN ADVANCE!!

[kevinSmith]

Do you have a repo for this? It would be easier than trying to set all this up.

[kevinSmith]

I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.

You can also use the “preformatted text” tool in the editor (</>) to add backticks around text.

See this post to find the backtick on your keyboard.
Note: Backticks (`) are not single quotes (’).

[kevinSmith]

I have tried a fetch method in task10.js and get an error fetch is not defined

I think with node, you might need to use a package like node-fetch.

How would I be able to get the exported elements from task10.js and test them in Jest after by having the following: …

Are you trying unit testing, integration testing, or end-to-end testing here?

To me, you start with unit testing. So, I would say that no function test should depend on a chain of events. Each function should be tested itself. If you need dummy data, then create it use that. You can also mock the functions that you want so each test is isolated to a specific case of a specific function.