Vue-test-utils using mixin for vee-validate in nuxt - vue.js

Question

I'm trying to test if validation works for a form with vee-validate and vue-test-utils. I also use nuxt and have created a custom plugin which install vee-validate and provides two custom computed properties as a mixin.
The problem is that I need a way to use these mixins within a localVue instance, however, I cannot just import the whole file as it results in vee-validate being installed two times on the main vue instance. I also cannot just say localVue.use(MyCustomVeeValidatePlugin) because the plugin doesn't have an install method ("plugins" in nuxt are somewhat different than in vue).
What works is creating a file which exports isFormValid and isFormChanged and then have the plugin import these methods. Then I also need to import these methods in the test file and create a mixin for the localVue instance. I would much rather prefer defining the mixin in a single plugin file. I know this is very specific but has anyone had a similar problem? I could imagine rewriting the plugin to be more like it is defined in the Vue.js docs (with an install method) and install it somehow.
Plugin:
import Vue from "vue";
import VeeValidate from "vee-validate";
Vue.use(VeeValidate);
//create global mixin for checking if form is valid
//note: every input element needs a name
Vue.mixin({
computed: {
isFormValid() {
return Object.keys(this.fields).every(key =>
this.fields[key].valid);
},
isFormChanged() {
return Object.keys(this.fields).some(key =>
this.fields[key].changed);
}
}
});

Answer 1

As far as I know, based on the recommendations I read in "Testing VueJs Applications (https://www.manning.com/books/testing-vue-js-applications), the author, who is also the main author of the vue-test-utils recommends:
I’ve already spoken about why you should use a localVue constructor and avoid installing on the base constructor. This is especially important for Vue Router. Always use a localVue to install Vue Router in tests. You must make sure that no file in your test suite imports a file that calls Vue.use with Vue Router. It’s easy to accidentally import a file that includes Vue.use. Even if you don’t run a module, if the module is imported, then the code inside it will be evaluated.
Based on that recommendation, I moved Vue.use() calls out of files like store.js and router.js and into main.js, which isn't used during testing.