If you have an Intel Mac, VMWare Fusion works really well for this! I have VMs of Lion, Mountain Lion, High Sierra, and Big Sur available at my fingertips withi

If you have an Intel Mac, VMWare Fusion works really well for this! I have VMs of Lion, Mountain Lion, High Sierra, and Big Sur available at my fingertips within VMware Fusion 8 running atop Mavericks. I do all of my development with VMs. It lets me instantly switch between xCode versions, and install dependencies without messing with the state of my real system. (P.S. I also have Tiger and Snow Leopard VMs, but this requires patching VMWare and is definitely not endorsed by Apple!)