Fix test, remove vue-filter relativeDateTime

cc @Tirokk @ulfgebhardt @appinteractive

This is a perfect example why I insist on writing tests. While debugging
@Tirokk and I discovered several design flaws and plugins that depend on
each other. The solution to all of this is not to use vue-filters plugin
at all! Vue-filters depends on Vuex, i18n, vuex-i18n, nuxt-modules and so
on.

This is just bad, bad, bad code. Start writing tests. Now.

We should start to refactor vue-filters and use components instead.

webapp/components/RelativeDateTime/index.spec.js

@@ -1,24 +1,52 @@
 import { shallowMount, createLocalVue } from '@vue/test-utils'
 import RelativeDateTime from './index.vue'
 
-import Filters from '../../plugins/vue-filters.js'
 const localVue = createLocalVue()
-localVue.use(Filters)
 
 describe('RelativeDateTime', () => {
   let wrapper
+  let mocks
+  let locale
 
   beforeEach(() => {
-    wrapper = shallowMount(RelativeDateTime, {
+    mocks = {
+      $i18n: {
+        locale: () => locale
+      }
+    }
+  })
+
+  let Wrapper = () => {
+    return shallowMount(RelativeDateTime, {
+      mocks,
       localVue,
       propsData: {
         dateTime: new Date()
       }
     })
-  })
+  }
 
   it('renders', () => {
-    console.log(wrapper.html())
-    expect(wrapper.is('span')).toBe(true)
+    expect(Wrapper().is('span')).toBe(true)
+  })
+
+  describe("locale == 'en'", () => {
+    beforeEach(() => {
+      locale = 'en'
+    })
+
+    it('translates', () => {
+      expect(Wrapper().text()).toContain('today at')
+    })
+  })
+
+  describe("locale == 'de'", () => {
+    beforeEach(() => {
+      locale = 'de'
+    })
+
+    it('translates', () => {
+      expect(Wrapper().text()).toContain('heute um')
+    })
   })
 })

webapp/components/RelativeDateTime/index.vue

@@ -3,6 +3,18 @@
 </template>
 
 <script>
+import formatRelative from 'date-fns/formatRelative'
+import { enUS, de, nl, fr, pt, es, pl } from 'date-fns/locale'
+const locales = {
+  en: enUS,
+  de,
+  nl,
+  fr,
+  es,
+  pt,
+  pl
+}
+
 export default {
   name: 'HcRelativeDateTime',
   props: {
@@ -13,7 +25,8 @@ export default {
   },
   computed: {
     relativeDateTime() {
-      return this.$filters.relativeDateTime(this.dateTime)
+      let locale = locales[this.$i18n.locale() || 'en']
+      return formatRelative(new Date(this.dateTime), new Date(), { locale })
     }
   }
 }

webapp/plugins/vue-filters.js

@@ -34,12 +34,6 @@ export default ({ app }) => {
         locale: getLocalizedFormat()
       })
     },
-    relativeDateTime: value => {
-      if (!value) return ''
-      return formatRelative(new Date(value), new Date(), {
-        locale: getLocalizedFormat()
-      })
-    },
     number: (
       value,
       precision = 2,