Return to menu unless all slides in a section are complete

You could do this:

• Create a T/F variable with a default value of False for each module. 
• Adjust the variable to True when the user completes the corresponding module.
• At the end of each module, have a trigger that shows a button to the assessment with the conditions that all of the variables = True.

I suggest you still show the button that returns to the menu, since some users might want to review content before taking the test.

It’s worth the effort to learn about variables and trigger conditions, because they provide the real power in Storyline. Here’s more information:

• This post provides an overview of variables. It also links to numerous resources.  The Value of Variables | Articulate - Community 
• The User Guide articles about triggers include some about conditions.  Storyline 360: Working with Triggers | Articulate - Community