Internet Explorer 7 is out and as the world gradually upgrades, our web applications are slowly forced into compliance if we want to truly reach all of our audience. When it's been declared that your app will support both (at least for the time being) the testers are forced to conduct browser compatibility using both. Because of this, testers are now dealing with the problem: Knowing that IE6 and IE7 can't be installed at the same time on one machine, what is the most efficient way to test both IE6 and IE7? It sure would be nice if I you could test both from a single test machine right? Fact of the matter is, you CAN! You've got two options here, a Not so Guaranteed way, and a Guaranteed way.

Not So Guaranteed Way
Use MultipleIEs from TredoSoft,which allows you have multiple versions of IE (3.0, 4.01, 5.01, 5.5, 6.0) placed and semi-runnable on one test system. I've done a bit of playing around with this method and from experience it's pretty unstable. IE is built to tie into your OS, so being a unstable seems reasonable when you have hacked apart piles of assemblies that make up different versions of IE (as MultipleIEs has done). If you're fairly familiar with what different versions of IE look and feel like you'll get the same uncomfortable hunch that I get when I'm trying to convince myself that I'm truly experiencing the version of browser I opened. Goofy things make me suspicious, like running IE 5.5 and viewing the "About" window which tells me that I'm running IE 6. Attempted validation of components in these browsers using detection tools such as BrowserHawk.com still leave me scratching my head due to issues with tools themselves or the browser. Who knows? I don't know! It would take a lot of work to know. I would find great comfort in proof that the rending engine, JavaScript version, management of cookies and cache of that browser were truly being used. But I don't have time to do that. Will you test on a questionable browser/system and put your "tested" seal on the Web app when you don't have proof of the authenticity of that browser? Not me. Those are my feelings, the IE team backs them up with this post. However, I can confidently put my seal on the Guaranteed Way:

Guaranteed Way
1. Install IE7 on your test machine.
2. Download and install the free Microsoft Virtual PC 2004 and the free Windows XP SP2 IE6 VPC Image (no license required). Set you new environment up in 19 easy steps.

Do it the right way testers. Microsoft has made it easy and free for you.