vue custom filter error in vue test utils

I am getting this error when running my test in vue-test-utils this.$options.filters.customCurrency is not a function

How can I either stub this as it's not needed or mock the function to prevent the error?

 Vue.filter('customCurrency', function (currency) {
    return currency
  });

component.vue

this.$options.filterks.customCurrency(this.currency)