Elsewhere in this forum, there was a discussion following the same basic question: can I use the competency rating in a similar way to the activity grading (and completion settings)? At this point, I would say the competencies approach can not be compared to the grading approach. With what Moodle presently provides for competencies, they're best used in an all-or-nothing way: you're either competent or you're not.
Having said this, it might make sense to break the relevant competency (or competencies) down into more useful bits, adding multiple levels of competency to the test (a basic behavior, an average behavior, an above average behavior and an expert behavior). These ratings should not be in the same competency, but should be treated as separate ones.
Then, breaking down the test into smaller units with a corresponding level of difficulty, will enable you to award 1 competency per test/quiz:
- basic test ==> basic competency
- average test ==> average competency
- above average test ==> above average competency
- expert test ==> expert competency
As for the other issue of how to handle the not-rated-yet competencies: I think the recommendation would be to find a clearer way to have them displayed. In the regular studyplans overview window for a student, it displays a progress bar that will fill according to the number of competencies rated in the plan. Unrated competencies are and should be left out. Competencies rated as not competent, do show up in the list, but not in the progress bar. Condition to fill the bar is: competency is rated as competent.
There is a lot of room for clarification and improvement in the way all this is displayed and how CBE is approached using Moodle, as you can see and read here... Hopefully this helps you in figuring out how to implement it all.