Karma unit test failing TypeError: undefined is not an object (evaluating ‘that.options.length’)

I have an AngularJS application that I’m trying my hand at unit tests, although I’m stuck at my first hurdle.

I keep getting the following error TypeError: undefined is not an object (evaluating 'that.options.length') when running the below controller and unit test.

I dont see where the undefined is and any help would be appreciated.

controller

function dropdownController() {
  const that = this;

  let selected = '';

  that.$onInit = () => {
    if (that.options.length) {
      selected = that.options.includes(that.default) ? that.default : that.options[0];
    }
  };
}

unit test

describe('Dropdown component', () => {
  // load the controller's module
  beforeEach(() => {
    angular.mock.module('app');
  });

  var $componentController, scope, component;

  // Initialize the controller and a mock scope
  beforeEach(angular.mock.inject(function ($rootScope, _$componentController_) {
    scope = $rootScope.$new();
    $componentController = _$componentController_;
    component = $componentController('dropdown', {$scope: scope});
    // component.$onInit();
  }));

  it('should set dropdown options on init', function () {
    let that = this;
    that.options = ['Tom', 'Dick', 'Harry'];
    component.$onInit();
    expect(that.options.length).toEqual(3);
  });
});

Source: AngularJS

from Angular Questions https://angularquestions.com/2017/10/11/karma-unit-test-failing-typeerror-undefined-is-not-an-object-evaluating-that-options-length/
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