Removed the tests since we are using defineCustomElement in IonTabs,

1. the slots are now being rendered within the shadow DOM and the tests don't have access to that
2. the rendering of the slots are based on the core components which is already being tested there

I found a few issues testing without a router. Steps to create the test app:

1. Create a new Ionic Vue tabs app: ionic start myVueTabsApp tabs --type=vue
2. Navigate to the app directory: cd ./myVueTabsApp
3. Install the dev build: npm i @ionic/vue@8.2.8-dev.11724095971.1e1b89ef @ionic/vue-router@8.2.8-dev.11724095971.1e1b89ef
4. Serve the app: ionic serve
5. Navigate to http://localhost:8100/ in the browser

Issue 1 - Undefined tab

1. Update src/App.vue to the following:

   <template>
     <ion-app>
       <ion-tabs>
         <ion-tab tab="tab1">
           <ion-content>Tab 1</ion-content>
         </ion-tab>
         <ion-tab tab="tab2">
           <ion-content>Tab 2</ion-content>
         </ion-tab>
   
         <ion-tab-bar slot="bottom">
           <ion-tab-button tab="tab1">
             <ion-icon :icon="triangle"></ion-icon>
             <ion-label>Tab 1</ion-label>
           </ion-tab-button>
           <ion-tab-button tab="tab2">
             <ion-icon :icon="ellipse"></ion-icon>
             <ion-label>Tab 2</ion-label>
           </ion-tab-button>
           <ion-tab-button tab="tab3">
             <ion-icon :icon="square"></ion-icon>
             <ion-label>Tab 3</ion-label>
           </ion-tab-button>
         </ion-tab-bar>
       </ion-tabs>
     </ion-app>
   </template>
   
   <script lang="ts">
     import { IonApp, IonContent, IonLabel, IonIcon, IonTabs, IonTab, IonTabBar, IonTabButton } from '@ionic/vue';
     import { ellipse, square, triangle } from 'ionicons/icons';
     import { defineComponent } from 'vue';
   
     export default defineComponent({
       components: { IonApp, IonContent, IonLabel, IonIcon, IonTab, IonTabs, IonTabBar, IonTabButton },
       setup() {
         return { ellipse, square, triangle };
       },
     });
   </script>

2. Refresh the browser
3. Click on "Tab 3"
4. Open the console and see error: tab with id: "undefined" does not exist
5. Compare this to a Vue tabs starter using router with a missing path for tab3 and it gives a warning: [Vue Router warn]: No match found for location with path "/tabs/tab3"
6. Removing the href from the 3rd <ion-tab-button> in the app with a router results in no warnings or errors in the console.

Issue 2 - Selected tab with href

1. Update src/App.vue to the following:

   <template>
     <ion-app>
       <ion-tabs>
         <ion-tab tab="tab1">
           <ion-content>Tab 1</ion-content>
         </ion-tab>
         <ion-tab tab="tab2">
           <ion-content>Tab 2</ion-content>
         </ion-tab>
         <ion-tab tab="tab3">
           <ion-content>Tab 3</ion-content>
         </ion-tab>
   
         <ion-tab-bar slot="bottom">
           <ion-tab-button tab="tab1" href="/tabs/tab1">
             <ion-icon :icon="triangle"></ion-icon>
             <ion-label>Tab 1</ion-label>
           </ion-tab-button>
           <ion-tab-button tab="tab2" href="/tabs/tab2">
             <ion-icon :icon="ellipse"></ion-icon>
             <ion-label>Tab 2</ion-label>
           </ion-tab-button>
           <ion-tab-button tab="tab3" href="/tabs/tab3">
             <ion-icon :icon="square"></ion-icon>
             <ion-label>Tab 3</ion-label>
           </ion-tab-button>
         </ion-tab-bar>
       </ion-tabs>
     </ion-app>
   </template>
   
   <script lang="ts">
     import { IonApp, IonContent, IonLabel, IonIcon, IonTabs, IonTab, IonTabBar, IonTabButton } from '@ionic/vue';
     import { ellipse, square, triangle } from 'ionicons/icons';
     import { defineComponent } from 'vue';
   
     export default defineComponent({
       components: { IonApp, IonContent, IonLabel, IonIcon, IonTab, IonTabs, IonTabBar, IonTabButton },
       setup() {
         return { ellipse, square, triangle };
       },
     });
   </script>

2. Refresh the browser
3. Click on the 3rd tab "Tab 3"
4. See that it switches to the 3rd tab correctly
5. Refresh the browser
6. See that "Tab 3" is still selected but the 1st tab "Tab 1" content is displayed

This is the same issue I reported when testing React without a router.

Issue 1: cc67360

Issue 2: 531ae5d