checking (reading) messages to console in js

Question

I'm creating unit tests using Qunit. I want to test that, for a non-fatal error, a warning message is sent to console. (Yes, I know we shouldn't be writing to console in production code. Let it go.)

So, I've got this popup utility that accepts a config object:

popup.js:

showPopup = function(cfg){
  if !(cfg.message){
    utils.log('A message is required!');
  }
};

(utils.log function will handle whether or not the browser actually supports console)

And then my tests file does its thing.

popup.tests.js:

showPopup({stuff: 'stuff', message: 'I am a popup!'});

QUnit.test('A warning message is logged to console', function (assert) {
  // want to know a message was sent
}

How can I confirm that the message was sent?

Answer 1

What I would do is override console.log in your unit test:

window.console = (function(old_logger) {
    var previous_message;
    var log = function(msg) {
        previous_message = msg;
        old_logger.log(msg);
    }
    var previous = function() {
        return previous_message;
    }
    return { log: log, previous: previous }
})(window.console);            

And then you can do:

showPopup({stuff: 'stuff'});
assert.equal('A message is required!', console.previous());

Answer 2

显然，对我们来说“正确”的答案是使用sinon stub。