To use the class:

my $duck = src::bo::Duck->new();
is( ref($duck), "src::bo::Duck", "A duck object" );
throws_ok { $duck->setFlyBehaviour( src::bo::CannotFly->new() ) }
  qr/setFlyBehaviour is protected/, "setFlyBehaviour is protected";
throws_ok { $duck->( "FLYBEHAVIOUR", src::bo::CannotFly->new() ) }
  qr/FLYBEHAVIOUR is protected/, "FLYBEHAVIOUR is protected";

#is( $duck->doFly(), "cannot fly", "the duck cannot fly" );

my $rubber = src::bo::Rubber->new();
is( ref($rubber),       "src::bo::Rubber", "A rubber duck object" );
is( $rubber->doFly(),   "cannot fly",      "the rubber duck cannot fly
+" );
is( $rubber->doQuack(), "can sqeek",       "the rubber duck sqeeks" );

my $whistle = src::bo::Whistle->new();
is( ref($whistle),       "src::bo::Whistle", "A whistle object" );
is( $whistle->doFly(),   "cannot fly",       "the whistle doesn't fly"
+ );
is( $whistle->doQuack(), "cannot quack",     "the whistle doesn't quac
+k" );

throws_ok { $whistle->setQuackBehaviour( src::bo::CanQuack->new() ) }
  qr/setQuackBehaviour is protected/, "setQuackBehaviour is protected"
+;
throws_ok { $whistle->( "QUACKBEHAVIOUR", src::bo::CanQuack->new() ) }
  qr/QUACKBEHAVIOUR is protected/, "QUACKBEHAVIOUR is protected";

$rubber->setColor("green");
is( $rubber->getColor(), "green", "it's a green rubber duck!" );
[download]

Ok, you have to imagine the 'use strict, use warnings, use Test::More, use Test::Exception, and all the use src::bo::somethings...