@testset "54.spiral-matrix.jl" begin
    @test spiral_order([[1, 2, 3], [4, 5, 6], [7, 8, 9]]) == [1, 2, 3, 6, 9, 8, 7, 4, 5]
    @test spiral_order([[1], [2], [3], [4], [5], [6], [7], [8], [9], [10]]) ==
          [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    @test spiral_order([[7], [9], [6]]) == [7, 9, 6]
    @test spiral_order([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]) ==
          [1, 2, 3, 4, 8, 12, 11, 10, 9, 5, 6, 7]
end
