test_coeff = ->
  run_test [

    "coeff(40*x^3+30*x^2+20*x+10,3)",
    "40",

    "coeff(40*x^3+30*x^2+20*x+10,2)",
    "30",

    "coeff(40*x^3+30*x^2+20*x+10,1)",
    "20",

    "coeff(40*x^3+30*x^2+20*x+10,0)",
    "10",

    "coeff(a*t^3+b*t^2+c*t+d,t,3)",
    "a",

    "coeff(a*t^3+b*t^2+c*t+d,t,2)",
    "b",

    "coeff(a*t^3+b*t^2+c*t+d,t,1)",
    "c",

    "coeff(a*t^3+b*t^2+c*t+d,t,0)",
    "d",
  ]