prove -v 1199413.pl
1199413.pl .. 
ok 1 - use Krautcat;
ok 2 - empty params throws ok
ok 3 - non-string param for constructor dies ok
ok 4 - assertion failure message looks ok
ok 5 - 'obj with valid constructor params' isa 'Krautcat'
ok 6 - attr has correct val from constructor
ok 7 - non-string param for qux() throws ok
ok 8 - string param for qux() validates ok
1..8
ok
All tests successful.
Files=1, Tests=8,  0 wallclock secs ( 0.01 usr  0.01 sys +  0.08 cusr  0.01 csys =  0.11 CPU)
Result: PASS