Help for Nunit Testing

Hello,

 

I'm new to Unit testing,I need help with writing a test for this method?? can anyone give me some idea?!

 

 

 
public void Withdraw(decimal amount)
{

Balance -= amount;
transaction = new Transaction();
transaction.Day = DateTime.Now.ToString("dd-MM-yy");
transaction.Type = Transaction.TransactionType.Withdraw;
transaction.Amount = -amount;
transaction.Total = Balance;
transactionList.Add(transaction);


}  ...