How to test a filter in VUE.js 2

testFilter.spec.js

/* component */

<script>
export default {
  name: 'sample',
  filters: {
    round: function (value) {
      if (!value) return NaN;
      return Math.round(value);
    }
  }
}
</script>

/* test */
import Vue from 'vue'
import Sample from '@/components/Sample'

describe('Sample component', () => {
  describe('#round filter', () => {
    const Constructor = Vue.extend(Sample);
    const Component = new Constructor().$mount();

    /* 
      here you access any of your component filter.
      
      filters are stateless and immutable, so don't
      worry about a single instantiation
    */
    
    const round = Component.$options.filters.round;

    // then test just like a plain simple function
    it("should round a number", () => {
      expect(round(3.14)).to.equal(3);
    });
  });
});