Many of us rely on VMware Fusion for testing our products both on older and newer versions of Mac OS X. Your development machine may be running Lion, but it’s incredibly handy to run both Snow Leopard and Mountain Lion on the same machine.
With the recent release of Mountain Lion DP2 some problems cropped up with Fusion 4.1 (you’ll need a developer account to view that link.) Luckily the new VMware Fusion Technology Preview 2012 makes it possible to run the latest Mountain Lion release without any problems. This preview release also allows you to keep Fusion 4.1 installed if you encounter any problems in other virtual machines: the only requirement is that you can only run one version at a time.
Also worth nothing: if you used the bug in VMware Fusion 4.1 to create a virtual machine that uses the client version of Mac OS X 10.6, you’ll be disappointed as soon as you try to restart that VM in the Technology Preview. During the reboot, you’ll see a window pop up with the message:
The guest operating system is not Mac OS X Server. This virtual machine will be powered off.
You’ll need to keep VMware Fusion 4.1 around if you want to apply Software Updates to your test environments.
I wish Apple would relax this restriction with the 10.6 clients: we still have products that rely on older versions of Xcode. Apple themselves even have sample code that can’t be opened in Xcode 4, preventing developers from exploring older, but useful, projects.