Refactor `a_count_occurrences_by_grade()` #464

All 849 tests pass, 11 skipped in 1m 12s

1 files ±0 84 suites ±0 1m 12s ⏱️ -1s
860 tests ±0 849 ✅ ±0 11 💤 ±0 0 ❌ ±0
1 847 runs ±0 1 161 ✅ ±0 686 💤 ±0 0 ❌ ±0

Results for commit 9da3fff. ± Comparison against earlier commit e4a7829.