gistfile1.rb

# how do you test algorithms?

class Pythagoream < Struct.new(:a, :b)
  class BadArgument < ArgumentError; end
  def result
    raise BadArgument if a < 0 || b < 0
    a**2 + b**2
  end
end

# I would probably test a few different aspects of this:
#   1. some simple cases, only caring about the known result
#   2. some edge cases (i.e. when an argument is zero)
#   3. error cases (i.e. when input is invalid)
context "Pythagoream" do
  should "return sum of squares" do
    assert_equal 8, Pythagoream.new(2, 2).result
    assert_equal 18, Pythagoream.new(3, 3).result
    assert_equal 25, Pythagoream.new(3, 4).result
    assert_equal 32, Pythagoream.new(4, 4).result
  end

  should "return square of one argument when the other is zero" do
    assert_equal 9, Pythagoream.new(3, 0).result
    assert_equal 9, Pythagoream.new(0, 3).result
  end

  should "return zero when both arguments are zero" do
    assert_equal 0, Pythagoream.new(0, 0).result
  end

  should "raise an exception if the first parameter is negative" do
    assert_raise(Pythagoream::BadArgument) do
      Pythagoream.new(-1, 4).result
    end
  end

  should "raise an exception if the second parameter is negative" do
    assert_raise(Pythagoream::BadArgument) do
      Pythagoream.new(3, -1).result
    end
  end
end