Adding args under last text added in .txt, discord.js

Question

I made this command that should add args to a txt file, and it works well, there's only one thing left i wanna do, when it adds a new text to the txt it adds it right after the last text, is it possible to make it add the text under it instead? This is what happens when i try to add something new, i want, in this case, the test 2 to be added under test:

const data = args.slice(0).join(" ");
        
    fs.appendFile('test.txt', data + " ", (err) => {  
        console.log('File edited')
        message.channel.send('test.txt updated')

    data.split('\n')

this is the code i made, hope you can help