If you switch from testing partnered dance to testing solo dance, you don't need to retake any pattern dances that you passed partnered. However, the pattern dances that you pass solo don't "count" towards partnered dance so you would have to retake any pattern dances that you passed solo to continue with partnered dance tests.
Partnered Dutch Waltz, solo Canasta, solo Rhythm Blues= solo Preliminary dance test; you can test solo Pre-Bronzes; you can't test patterned Pre-Bronzes - you would have to test and pass the Canasta and Rhythm Blues partnered before testing any partnered Pre-Bronzes.