void circle_area()
        {
            context["when radius is 1"] = () =>
                                          it["result is pi"] = () =>
                                                               target.AreaOfCircle(1)
                                                               .ShouldBe(Math.PI);

            context["when radius is 5"] = () =>
                                          it["result is 25*pi"] = () =>
                                                                  target.AreaOfCircle(5)
                                                                  .ShouldBe(25 * Math.PI);
        }