The test started failing in commit 7d7f62e, but this was not detected
due to no automatic test environment. The commit changed the cell
numbering from "per-column (K,I,J)-ordering" to "per-plane
(I,J,K)-ordering". Consequently, the "correct_answer" seized to be
correct.
This change restores the "correct_answer" in the ordering introduced by
commit 7d7f62e.
While here, adjust style of the DisjointColumn test case for legibility.