message: increase coverage for UnderlineNav tests
diff: @@ -70,4 +70,9 @@ describe('Caret', () => {
  'data-active-class': SELECTED_CLASS
  })
  })
  +
  + it('does not add duplicate ITEM_CLASS classes', () => {
  + const wrapper = mount(<UnderlineNav><span className={ITEM_CLASS} /></UnderlineNav>)
  + expect(wrapper.find('span').props().className).toEqual(ITEM_CLASS)
  + })
  })
  