is eval { $o->answer }, 42, 'answer returned 42'

I've used this on occasion, but I've three issues with the idiom. First, when undef is a legal return value it's of no use. Second, you don't get to see the error message on failure. Third, you can't tell the difference between failure due to an exception and failure due to returning undef.

is do {
   lives_ok {$o->answer} 'answer worked'
}, 42, 'answer returned 42';
[download]

We're back to two tests - and it doesn't work :-)

... but only because I lied in my example... bad adrian...

lives_ok returns a boolean, not the result of the coderef. This is usual for test subroutines so that you can use the do_some_test(...) || diag(some message) idiom.