Is a second license required?

[Fabsboards]

I'd like to set up a private test board. The sole purpose would be to test new mods before installing in my forum.

Is a second license required for this?

[R1lover]

Nope, test boards are fine as long as there not live.

[Antivirus]

they also need to be in a password-protected directory named \testvb

There's specific guidelines to follow for setting up a test forum which you can read in the user license agreement located within the vbulletin member's area.