fix: allow plugins to be re-installed in localVue instance

close vuejs#406

Author: kellym

src/create-local-vue.js

@@ -32,6 +32,7 @@ function createLocalVue (): Component {
   instance.options._base = instance
 
   // compat for vue-router < 2.7.1 where it does not allow multiple installs
+  instance._installedPlugins = []
   const use = instance.use
   instance.use = (plugin, ...rest) => {
     if (plugin.installed === true) {

test/specs/create-local-vue.spec.js

@@ -1,4 +1,5 @@
 import { createLocalVue } from '~vue-test-utils'
+import Vue from 'vue'
 import Vuex from 'vuex'
 import Vuetify from 'vuetify'
 import VueRouter from 'vue-router'
@@ -97,6 +98,13 @@ describe('createLocalVue', () => {
     expect(typeof freshWrapper.vm.$route).to.equal('undefined')
   })
 
+  it('installs Router regardless of global Vue', () => {
+    Vue.use(VueRouter)
+    const localVue = createLocalVue()
+    localVue.use(VueRouter)
+    expect(VueRouter.install.installed).to.equal(true)
+  })
+
   it('use can take additional arguments', () => {
     const localVue = createLocalVue()
     const pluginOptions = { foo: 'bar' }