所以要测试相当于这个模板{{foo | testFilter：capitalize}}

describe('The test filter',function () {
  'use strict'; 

  var $filter;

  beforeEach(function () {
    module('myTestFilterModule');

    inject(function (_$filter_) {
      $filter = _$filter_;
    });
  });

  it('should capitalize a string',function () {
    // Arrange.
    var foo = 'hello world',result;

    // Act.
    result = $filter('testFilter')(foo,'capitalize');

    // Assert.
    expect(result).toEqual('HELLO WORLD');
  });
});