our Account class:</p>

<div class="code"><pre class="prettyprint">private decimal minimumBalance = 10m;

public decimal MinimumBalance
{
  get{ return minimumBalance; }
}</pre>
</div>

<p>We will use an exception to indicate an overdraft:</p>

<div class="code"><pre class="prettyprint">namespace Bank
{
  using System;

  public class InsufficientFundsException : ApplicationException
  {
  }
}</pre>
</div>

<p>Add a new test method to our AccountTest class:</p>

<div class="code"><pre class="prettyprint">[T