Testing an Object
Some objects understand messages that answer boolean true or false values. You can use these to test to see if an object is of a particular kind or in a particular state. Try these examples:
'this is not an integer' isInteger.
5 between: 0 and: 10.
charlie respondsTo: #>=.
This last expression asks to see if charlie can understand a #>= message. We've already seen above that it can't so the false answer comes as no surprise.
Tip: many testing messages take the form #isXXX. You'll find that this helps to make code easy to read and also gives an indication that the message will answer a boolean value.