How to provide mock files to change event of <input type='file'> for unit testing

Issue

I'm having difficulties with a unit test in which I want to verify the processing of a file, which would usually be selected in the view via <input type='file'>.

In the controller part of my AngularJS app the file is processed inside the input's change event like so:

//bind the change event of the file input and process the selected file
inputElement.on("change", function (evt) {
    var fileList = evt.target.files;
    var selectedFile = fileList[0];
    if (selectedFile.size > 500000) {
        alert('File too big!');
    // ...

I'd like evt.target.files to contain my mock data instead of the user's selected file in my unit test. I realized that I can't instantiate a FileList and File object by myself, which would be the according objects the browser is working with. So I went with assigning a mock FileList to the input's files property and triggering the change event manually:

describe('document upload:', function () {
    var input;

    beforeEach(function () {
        input = angular.element("<input type='file' id='file' accept='image/*'>");
        spyOn(document, 'getElementById').andReturn(input);
        createController();
    });

    it('should check file size of the selected file', function () {
        var file = {
            name: "test.png",
            size: 500001,
            type: "image/png"
        };

        var fileList = {
            0: file,
            length: 1,
            item: function (index) { return file; }
        };

        input.files = fileList; // assign the mock files to the input element 
        input.triggerHandler("change"); // trigger the change event

        expect(window.alert).toHaveBeenCalledWith('File too big!');
    });

Unfortunately, this causes the following error in the controller which shows that this attempt failed because the files were not assigned to the input element at all:

TypeError: 'undefined' is not an object (evaluating 'evt.target.files')

I already found out that the input.files property is read-only for security reasons. So I started another approach by dispatching a customized change which would provide the files property, but still without success.

So long story short: I'd be eager to learn a working solution or any best practices on how to approach this test case.

Solution

Let's rethink AngularJS, DOM must be handled in a directive

We should not deal with DOM element in a controller, i.e. element.on('change', .., especially for testing purpose. In a controller, You talk to data, not to DOM.

Thus, those onchange should be a directive like the following

<input type="file" name='file' ng-change="fileChanged()" /> <br/>

However, unfortunately, ng-change does not work well with type="file". I am not sure that the future version works with this or not. We still can apply the same method though.

<input type="file" 
  onchange="angular.element(this).scope().fileChanged(this.files)" />

and in the controller, we just simply define a method

$scope.fileChanged = function(files) {
  return files.0.length < 500000;
};

Now, everything is just a normal controller test. No more dealing with angular.element, $compile, triggers, etc.! :)

describe(‘MyCtrl’, function() {
  it('does check files', inject(
    function($rootScope, $controller) {
      scope = $rootScope.new();
      ctrl = $controller(‘UploadCtrl’, {‘$scope’: scope});

      var files = { 0: {name:'foo', size: 500001} };
      expect(scope.fileChanged(files)).toBe(true);
    }
  ));
});

http://plnkr.co/edit/1J7ETus0etBLO18FQDhK?p=preview

Answered By - allenhwkim