@testset "Propagator" begin

  using PlotlyJS: savefig

  println("Testing Propagator")

  # Set up
  start_mass = 10_000.
  start = gen_orbit(rand(.5year : hour : 2year), start_mass)
  time = rand(0.2year : second : 0.5year)
  n = 1_000

  # Test that Propagation works
  states = prop(zeros(n,3), start, no_thrust, time)
  @test states[1,:] != states[end,:]

  # Test that mass is reduced properly
  states = prop(ones(n,3)/√3, start, bepi, time)
  @test states[end,7] ≈ start_mass - mfr(bepi)*time

  # Test that the propagator works backwards
  backwards = prop(ones(n,3)/√3, states[end,:], bepi, -time)
  p = plot([states, backwards])
  savefig(p,"../plots/prop_back.html")
  @test backwards[end,:] ≈ start

end