Spying on console.error() with Jasmine

Question

I'm actually new to JavaScript as well as Jasmine. So it might be something really obvious that fixes my problem but I can't see it.

I want to check if (an already existing) JavaScript application calls console.error() while loading. I don't really see a way how to realise this with Jasmine. I've included the JavaScript file as well as the spec file in the SpecRunner.html . But I take it that I somehow need to "instantiate" the application in order to test if it throws any errors on the console, right?

Or should I include the SpecRunner.html code only for this purpose into the HTML code of the app?

Answer 1

You can spy on console.error like this:

beforeEach(function(){
  spyOn(console, 'error');
})

it('should print error to console', function(){
  yourApp.start();
  expect(console.error).toHaveBeenCalled();
})

Answer 2

You can override the standard console.error function like this:

//call the error function before it is overriden
console.error( 'foo' );

//override the error function (the immediate call function pattern is used for data hiding)
console.error = (function () {
  //save a reference to the original error function.
  var originalConsole = console.error;
  //this is the function that will be used instead of the error function
  function myError () {
    alert( 'Error is called. ' );
    //the arguments array contains the arguments that was used when console.error() was called
    originalConsole.apply( this, arguments );
  }
  //return the function which will be assigned to console.error
  return myError;
})();

//now the alert will be shown in addition to the normal functionality of the error function
console.error( 'bar' );

This solution works with Jasmin or anything else. Just put the code above before the other codes and any call after this to console.error() will call the overridden function.

Answer 3

使用toThow和toThrowError http://jasmine.github.io/edge/introduction#section-Spies:_和and.throwError