How to use the yeoman-generator.test.assertFiles function in yeoman-generator

it('creates expected files', function () {
      var expected = [
        'index.html',
        'js/app.js',
        'css/style.css',
        'Gruntfile.js',
        'package.json',
        'bower.json'
      ];

      helpers.assertFiles(expected);
    });

this.app.run({}, function () {
            helpers.assertFiles(expected);
            done();
        });
    });

this.app.run({}, function () {
          helpers.assertFiles(expected);
          done();
        });
      });

this.app.run({}, function () {
            helpers.assertFiles(expected);
            done();
        });
    });

klei.run({}, function () {
      helpers.assertFiles(expected);
      done();
    });
  });

this.model.run({}, function () {
      helpers.assertFiles( JS_FILES_GENERATED_BY_MODEL_SUBGEN );
      helpers.assertFile('app/scripts/models/user_model.js', /User = DS.Model/);
      helpers.assertFile('app/scripts/models/user_model.js', /name: DS.attr\('string'\)/);
      helpers.assertFile('app/scripts/models/user_model.js', /zipcode: DS.attr\('number'\)/);
      helpers.assertFile('app/scripts/models/user_model.js', /User.FIXTURES/);
      done();
    });
  });

router.run({}, function () {
      helpers.assertFiles([router.options.router_file]);
      done();
    });
  });

this.module.run({}, function() {
        helpers.assertFiles([
          'app/modules/Foo/main.js',
          'app/modules/Foo/main.styl'
        ]);
        done();
      });
    });

this.chromeapp.run({}, function () {
        helpers.assertFiles(expected);
        done();
      });
    });

this.app.run({}, function () {
            helpers.assertFiles(expected);
            done();
        });
    });