As part of writing the unit tests for bm->write(), we have found a potential test case that is complex and deserves a separate ticket. The idea behind this ticket is to create test cases the expected behavioural differences between best fit vses first fit. The test would make sure that the best fit always chooses the correct blocks as the "best-fit", and make sure that the "first fit" option makes sure that the first fittable block is chosen as the block to be written.