Quoting stan shepherd squeak414@free.fr:
It is considered bad when isKindOf: is used in the following way:
(anObject isKindOf: String) ifTrue: [anObject size]
It is good design to let an object decide what to do when it recieves a message, rather than using isKindOf: to decide whether you should send an object one message and not another. The reason being that, someone may want to use a different kind of object that respects the String protocol.
Objects are better classified by what messages they respond to, not what class they may be.
For unit tests, this is a good use for it, though.
Once you have established that the signaled message is not in fact an error, is it possible to tell code critics not to signal that message for that code in subsequent runs?
...Stan