Smalltalk and Object Orientation: an Introduction - Free

22.7.2 The Perform: message
The perform message takes a symbol as its parameter. It then uses this symbol as the name of a method
to execute on the receiving object. As the symbol can be stored in a variable, it is impossible to
determine all the possible symbol va lues which will be passed to the perform message. It is therefore
advisable not to use perform unless it is absolutely necessary. However, if the developer has used a
perform expression, then a reasonable set of tests should be identified. Once again, the assumptions
used to generate this set should be made explicit.
22.8 Summary
In this chapter we have considered some of the special problems which face a developer when testing an
object oriented system (with special consideration for Smalltalk implementations) . As has been
discussed inheritance, abstraction, polymorphism and encapsulation all play a major part in determining
the best practice in testing Smalltalk systems. A number of recurring themes have been:
• The importance of specifying what a class or object is intended to do.
• The use of scenarios to aid in the adequate testing of methods and classes.
• The adequacy of testing and the importance of deciding what is sufficient.
• Examples and assumptions need explanation (including their context).
A final comme nt is that this chapter should not put you off constructing large complex systems in
Smalltalk. Rather it should make you aware of the difficulties you will face in testing such a system.
22.9 Further reading
Little has been written about the special problems o f testing object oriented systems, however the
papers by [Barbey and Strohmeier 1994] and [Barbey, Amman and Strohmeier 1994] are an exception
and provide an excellent introduction to the subject of testing object oriented systems. [Perry and Kaiser
1990] a discussion of the effects of inheritance on object oriented testing. The next chapter also
provides further reading on the subject of object oriented testing.
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