How to dual-boot Mac: run two versions of macOS on a Mac

Want to run two versions of macOS on your Mac? Here’s how to dual-boot macOS Mojave and an older version of macOS, or a beta version, on the same Mac. This is a great way to try out a beta version of macOS without breaking anything
How to dual-boot Mac: run two versions of macOS on a Mac
Source: Mac World How To