The heavy vehicle tests contain the official NZTA questions for the class 2 and class 3-5 learner licence test plus a number of questions that cover additional rules not covered in the learner licence test.
What you need to know to pass your heavy vehicle learner licence
It's best to work your way through the individual modules. If you're doing Class 2, then do the Class 2 questions, then all the other modules (ignore the Class 3-5 questions). Once you're sure you've got 100% in each question (you'll see this because it'll be tracked in the interface), try some random tests to make sure you're getting 100% when the questions are randomised.
If you're taking Class 3 or 5, then you'll need to know the Class 2 questions, too. Make sure you take all the modules individually, then try random 35-question tests. There is no theory test for class 4.
Any test you complete will be stored to your profile.