test_erf = ->
  run_test [

    "erf(a)",
    "erf(a)",

    "erf(0.0) + 1",
    "1.0",

    "float(erf(0))",
    "0.0",

    "erf(0.0)",
    "0.0",

    "erf(-0.0)",
    "0.0",

    "erf(0)",
    "0",

    "erf(-0)",
    "0",

    "float(erf(0)) + 1",
    "1.0",

    "float(erf(1))",
    "0.842701...",

  ]