test_arctan = ->
  run_test [

    "arctan(x)",
    "arctan(x)",

    "arctan(-x)",
    "-arctan(x)",

    "arctan(0)",
    "0",

    "arctan(tan(x))",
    "x",

    "arctan(1/sqrt(3))-pi/6",  # 30 degrees
    "0",

    "arctan(1)-pi/4",    # 45 degrees
    "0",

    "arctan(sqrt(3))-pi/3",    # 60 degrees
    "0",

    "arctan(a-b)",
    "arctan(a-b)",

    "arctan(b-a)",
    "-arctan(a-b)",

    "arctan(tan(x))",
    "x",
  ]