Is there a function to detect if a page is iframed?

ex.

<div align="center">
<IFRAME name="iframe_name" id="iframe_id" src="test.htm" scrolling="no" width="550" height="410" frameborder="0">
</IFRAME>
</div>

How to check inside 'test.htm' if test.htm is placed in a iFrame?

Tx