Check out this official Microsoft site!
Microsoft provides free virtual machines for developers to use, to develop for IE and Edge. And just to develop in general.
Currently, you can choose between Windows 7, 8 and 10 VMs. All but Windows 10 are just x86 (32bit) though. You can also choose between IE 8, 9, 10 and 11. Windows 10 being the exception, as it comes with Edge on x64.
What’s nice is that they package the VMs for different kinds of virtual machine applications, including VirtualBox, VMware, Hyper-V, Vagrant and Parallels.
Of course this does not include a Windows license, and the test version expires after 90 days. But you can “rearm” the test version multiple times, enough time for testing things out. You can also always enter a valid license and activate the VM, though.
It’s also handy to have one of those to run or test less-trusted applications, and then dispose of the VM.