Design an oracle for the following JavaScript function

[Gatayo]

Design an oracle for the following JavaScript function.
2. Generate a test case set for this function and provide a coverage analysis report for your test case set.

The JavaScript function:

function purchaseSong(username, password, songId) {
 
  // first authenticate the user
  if (checkCredentials(username, password) == false) {
    alert('The username or password is incorrect.');
    return;
  }
 
  // get the price of the song
  var songPrice = getSongPrice(songId);
 
  // make sure the user has enough money in his account
  if (getAccountBalance(username) < songPrice) {
    alert('You do not have enough money in your account.');
    return;
  }
 
  // debit the user's account
  debitAccount(username, songPrice);
 
  // start downloading the song to the client machine
  downloadSong(songId);
}

Notice: You may note that the user could be malicious and try to modify the JavaScript. Your oracle and test case should reflect this fact.

[Ezzaral]

Ok congratulations, you've demonstrated that you can paste your homework. Do you have any specific questions? Anything at all to show that you have given this the least bit of thought?

[Gatayo]

I have already solved the problem, I just wanted to compare my solution to others and see if there would some similarities in the way of approaching the problem