It’s always been a pain testing a website on Internet Explorer, especially if you only have a Mac to hand. I had heard that virtual PC environments are available to run Windows on a Mac, but presumed it would take a lot of effort to buy an installation of Windows and set it all up.
While it is a shame that Microsoft built recent versions of Internet Explorer in the first place, they have come good and produced free virtual images of IE running on Windows, in something called the modern.ie project.
I originally downloaded the IE9 image, thinking that if I could get things running on IE9 surely they would just about run on IE11. And each image is 5GB so you may not want to download too many. But then I remembered that more recent versions of IE (including version 9 really) have much better development tools, including ways to test against previous versions of the browser. So I think version 11 would have left me with more options really.
Also, the script suggested on OSX Daily attempts to download the 5GB image from the command line, which may be fine depending on your internet connection, but if it’s likely to be interrupted, maybe try using a file download manager for that part. It’s easy enough to see where the script was trying to download the file, so stop the script, download the file separately into the right location, then run the script again.