Add a range of data-testid tags to be able to cleanly identify parts of the application.

src/home/JoinExistingCallModal.tsx

@@ -43,7 +43,7 @@ export function JoinExistingCallModal({ onJoin, onClose, ...rest }: Props) {
         <p>{t("This call already exists, would you like to join?")}</p>
         <FieldRow rightAlign className={styles.buttons}>
           <Button onPress={onClose}>{t("No")}</Button>
-          <Button onPress={onJoin}>{t("Yes, join call")}</Button>
+          <Button onPress={onJoin} data-testid="home_joinExistingRoom">{t("Yes, join call")}</Button>
         </FieldRow>
       </ModalContent>
     </Modal>