How to set up test that picks only one entire question bank?

Hi, Charlotte.

Thank you for reaching out!

My suggestion for you would be to create a random variable (let's call it Quiznumber) with number values from 1 to 3. 

When the learner clicks the button to start the quiz, depending on the value of the variable, they will be taken to a specific draw from the question bank:

When you publish for LMS, you can track all three exams. The way multiple completion criteria works is whichever option a learner completes first is the one that gets reported to your LMS. (Only one option gets sent to the LMS, even if a learner completes multiple criteria.):

The article below will give you additional information on multiple completion criteria:

• Storyline 360: More Quizzing and Tracking Options

I hope this helps!