@testset "Non-allocating functions" begin
  f! = (f_x, x) -> (f_x[1] = x[1]^2 - 2x[2]^2; f_x)
  Jf! = (Jf_x, x) -> (Jf_x[1] = 2x[1]; Jf_x[2] = -4x[2]; Jf_x)
  Hf! = (Hf_x, x) -> begin
    Hf_x[1, 1] = 2.0
    Hf_x[1, 2] = Hf_x[2, 1] = 0.0
    Hf_x[2, 2] = -4.0
    Hf_x
  end

  size_f_x = (1,)
  size_Jf_x = (1, 2)
  size_Hf_x = (2, 2)

  f_x = zeros(size_f_x...)
  Jf_x = zeros(size_Jf_x...)
  Hf_x = zeros(size_Hf_x...)

  x = rand(2)

  @test TaylorTest.check!(f!, Jf!, x, size_f_x, size_Jf_x)
  @test TaylorTest.check!(Jf!, Hf!, x, size_Jf_x, size_Hf_x)
end