No matter how many old OS X installers you end up keeping on your backup data drives, trying to create legacy systems for development testing can be more of a pain than I expected. Recent versions of OS X do everything they can to prevent downgrades, I did better installing early releases onto fresh partitions and upgrading them.
This explains why I just wasted an entire morning creating and upgrading Lion partitions to enable me to have some fresh 10.7, 10.8, and 10.9 on-hand. Fortunately, I long ago wrote up a how-to for creating a stand-alone USB installer stick for TUAW, back when TUAW still existed. I was thrilled to find that stick exactly as I left it because it was the thing that let me boot one of my Yosemite systems (still running Beta 4, apparently) to a suite of tools that actually allowed me to install these OS’s. Yosemite’s recovery partition was not as accommodating.
I set up a fresh USB drive with many partitions, installed Lion into one of them and then cloned that into the other partitions. From there, it was just a matter of having the right upgrades on-hand. (I had them all except Mavericks, but Mike Ash, bless him, pointed out that I could grab a copy from App Store from my old purchases.)
I know there are lots of other solutions including virtual machines and such, but I like having native systems running on native hardware, using a bootable USB hard drive that can move from machine to machine to machine.
I’m still waiting on my Mavericks upgrade but soon my test systems will be all back in shape, even those I thoughtlessly yozed last Summer.