test all sizes
    0, 1, 2, 3, 4, many
test boundary cases

test [5,5,5,5,1,5,5,5,5]
test [5, 1, 2, 3, 4, 1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]
[5, 4, 3, 2, 1]