title: Mock file input for unit test
body: <p>I got something like these lines of code:</p>
  
  <pre><code>jQuery('.js-img-input').on('change', handleNewFiles);   
  
  var handleNewFiles = function(event) {
      var fileList = event.target.files;
      loadFileList(fileList);
  };
  
  var loadFileList = function(fileList) {
      jQuery(fileList).each(function(key, file) {
          readFileAsync(file);
      });
  }
  
  var readFileAsync = function(file) {
      var fileReader = new FileReader();
      fileReader.addEventListener("load", function(event) {
          file.result = event.target.result;
          saveFile(file);
      });
      fileReader.readAsDataURL(file);
  };
  </code></pre>
  
  <p>All of the methods are private inside a jQuery-function and I don't whant to make "handleNewFiles" public just for testing purpose.<br>
  I would love to test these lines with something like this:</p>
  
  <pre><code>it('should create a fileReader', function(){
      spyOn(window, 'FileReader').and.returnValue({
          addEventListener: function(){},
          readAsDataURL: function(){}
      });
      jQuery('.js-img-input').trigger('change');
      expect(window.FileReader).toHaveBeenCalled();
  });
  </code></pre>
  
  <p>But how did I get some dummy data into <strong>event.target.files</strong>?</p>