title: How to change vuex getter value in vue testing?
body: <p>I have this simple test:</p>
  
  <pre><code>describe('App', () =&gt; {
      let store;
      beforeEach(() =&gt; {
          store = new Vuex.Store({
              modules: {
                  auth: {
                      namespaced: true,
                      getters: {
                          isLoggedIn: () =&gt; true,
                      }
                  }
              }
          });
      });
  
      test('App hides navbar when user is logged in', () =&gt; {
          const wrapper = shallowMount(App, { store, localVue });
          expect(wrapper.contains(Nav)).toBe(false);
  // store.getters['auth/isLoggedIn'] = () =&gt; false; // Not possible
      });
  });
  </code></pre>
  
  <p>But I can't change the getter value and I am seeing this error in the console:</p>
  
  <blockquote>
    <p>TypeError: Cannot set property auth/isLoggedIn of # which has only a getter</p>
  </blockquote>
  
  <p>How do I set the getter value in my test?</p>