test_split_1: all good (2900 good bases)
test_split_2: 1000 good bases, then 50 bad bases, then 1850 good bases
test_split_3: 1000 good bases, then 100 bad bases, then 1800 good bases
test_split_4: 1000 good bases, then 200 bad bases, then 1700 good bases