There are several ways to test if HA is working. You can unplug the power of your server or perform a reset of the machine and a fail over will take place. In training classes and for demo's it's nicer if you can actually have the server to crash and show a Purple Screen of Death (PSOD).
This is the command to execute:
vsish -e set /reliability/crashMe/Panic 1
And this is the result: