Fix console.errors

@mattwr18 @alina-beck there seems to be no switch or configuration to
let vue-test-utils or jest fail whenever there is a call to
`console.error`. The only way to test it for very specific tests is
this. I took it from here:

https://geedew.com/catching-prop-validation-in-vue-with-Jest/

webapp/components/PostTeaser/PostTeaser.spec.js

@@ -22,11 +22,13 @@ describe('PostTeaser', () => {
     propsData = {
       post: {
         id: 'p23',
+        disabled: false,
+        shoutedCount: 0,
+        commentsCount: 0,
         name: 'It is a post',
         author: {
           id: 'u1',
         },
-        disabled: false,
       },
     }
     stubs = {
@@ -63,6 +65,13 @@ describe('PostTeaser', () => {
       })
     }
 
+    it('has no validation errors', () => {
+      const spy = jest.spyOn(global.console, 'error');
+      Wrapper()
+      expect(spy).not.toBeCalled()
+      spy.mockReset()
+    })
+
     beforeEach(jest.useFakeTimers)
 
     describe('test Post callbacks', () => {
@@ -111,6 +120,7 @@ describe('PostTeaser', () => {
     describe('given a post', () => {
       beforeEach(() => {
         propsData.post = {
+          ...propsData.post,
           title: "It's a title",
         }
       })