It still exists. As you have an Early 2011 MacBook Pro, Apple Hardware Test comes installed on the hard disk (if you upgraded OS X, it has disappeared) and on the Mac OS X disc that came with the Mac.
To start into Apple Hardware Test, insert the Mac OS X disc that came with your computer, and press D key while your Mac is starting. On newer Macs, just press Option and D keys while the computer is starting. See > http://support.apple.com/kb/HT1509
Just an FYI..... the Option key is not necessary with newer Macs. Just the D key needs to be pressed. As stated in the article #2 mentions in the Note how it works. This is exactly how it works with my 2012 model.
2. Press and hold the D key before the gray startup screen appears. If Apple Hardware Test does not start up, see the Additional Information section at the end of this article.
Note: Some Macintosh computers that shipped with OS X Lion and later support the use of Apple Hardware Test over the Internet. These computers will start up to an Internet-based version of AHT if the hard drive does not contain AHT. An Internet-enabled connection via Ethernet or Wi-Fi is required to use this feature.