Want to test transfer method using neo-gui-developer

[webplusai]

I want to invoke transfer method which is as following.

public static bool Transfer(StorageContext context, byte[] from, byte[] to, BigInteger amount)
{
            if (from.Length != 20 || to.Length != 20) return false;
            if (amount <= 0) return false;
            if (!Runtime.CheckWitness(from)) return false;
            if (from == to) return true;

            BigInteger fromBalance = Storage.Get(context, from).AsBigInteger();
            if (fromBalance < amount) return false;
            if (fromBalance == amount)
                Storage.Delete(context, from);
            else
                Storage.Put(context, from, fromBalance - amount);

            BigInteger toBalance = Storage.Get(context, to).AsBigInteger();
            Storage.Put(context, to, toBalance + amount);
            Transferred(from, to, amount);
            return true;
}

method invoke is not succeeded because it stops at line 5 if (!Runtime.CheckWitness(from)) return false;, which always returns false.

How can I make CheckWitness return true?
Thanks for help in advance.