Mage2\User\Models\User::isInWishlist PHP Method

    public function isInWishlist($productId)
    {
        $wishList = Wishlist::where('website_id', '=', $this->websiteId)->where('user_id', '=', $this->attributes['id'])->where('product_id', '=', $productId)->get();
        if (count($wishList) <= 0) {
            return false;
        }
        return true;
    }