I think you will find 80% of the problems if you test your app with any browser (see 80–20 rule). Said that, I also test with IE.
There are a few better ways to test with IE on a Mac than installing IE for Mac:
- Install Windows in a virtual machine with:
- VirtualBox (free)
- VMware Fusion (30-day free trial, then 63.23 USD)
- Parallels (did not use it, looks like they have 14-day free trial and then 79.99 USD)
- Install Windows on your Mac machine with Boot Camp
If you pick dual boot or virtual machine you will have to buy Windows too. (Upgrade from a previous Windows version is 39.99 USD, could not find out how much the full version costs.)
- Use a cloud service that will run IE for you:
- Sauce Labs (free account provides testing Windows for 100 minutes automated + 30 minutes manual every month, paid plans start with 12 USD/month)
- TestingBot (free account provides testing for 100 minutes in the first two weeks, paid plans start with 40 USD/month)
MediaWiki (software that runs Wikipedia) has a few Watir tests that drive Chrome, Firefox and IE on Sauce Labs, the code is at github.com/wikimedia/qa-browsertests.