That should be pretty clear. Look at the new test now. Use the throws_ok  
     test from Test::Exception to test the Carp::croak(). Using Test::Most  
     instead of Test::More makes this test function available without explicitly
     using Test::Exception.

     sub full_name : Tests(no_plan) {
         my $test   = shift;
         my $person = $test->class->new;
         can_ok $person, 'full_name';
 
         throws_ok { $person->full_name }
             qr/^Both first and last names must be set/,
             '... and full_name() should croak() if the either name is not set';