title: How to find path of active app.config file?
body: <p>I'm trying to finish this exception handler:</p>
  
  <pre><code>if (ConfigurationManager.ConnectionStrings["ConnectionString"]==null)
  {
      string pathOfActiveConfigFile = ...?
      throw new ConfigurationErrorsException(
         "You either forgot to set the connection string, or " +
         "you're using a unit test framework that looks for  "+
         "the config file in strange places, update this file : " 
         + pathOfActiveConfigFile);
  }
  </code></pre>
  
  <p>This problem seems to only happen to me when I'm using nUnit.</p>