Smalltalk and Object Orientation: an Introduction - Free

23.1.6 Tracing a classes operation
In order to trace a classes operation it would be possible to create a subclass which mirrored the parent
classes methods exactly. The subclasses methods could print the value of any parameters into the
method before calling the method and then any results returned by the method. If necessary tests could
be performed to ensure that the parameters or the returned value were within ant icipated ranges. The
advantage of testing the class method calls in this way would be to encapsulate all the test information
into a test subclass which could be removed from the Smalltalk image for the delivered system.
23.1.7 Sources of test information
The con cept of use cases discussed earlier in this book is an important source of test cases.
Opportunities for the merging of the use case specifications into test specifications abound.
A style issue, rather than a testing issue, is that it is good style to pro vide a set of test examples,
often on the class side, which exercise some behavior of the objects of the class. These can be used to
illustrate how to use the objects of the class. They can also act as a form of regression testing either
when the class is modified or when a subclass is defined. If these test methods are placed in appropriate
protocols, then the whole protocol can be filed out in one go, thus creating a test file.
23.2 Object integration testing
The above section deliberately only deals with the issue of testing a class in isolation. This involves
individual method testing followed by testing combinations of methods. Object integration testing
involves testing instances of the same or different classes when they are collaborating in some
operation. This is different from traditional procedural integration testing as the structure of traditional
programming languages is fairly rigid and is unlikely to vary while the system is executing. It is also
different from statically bound procedural programs, because when a language such as Pascal is used,
the compiler is able to test to see whether the called procedure or function definition matches the calling
definition. For example, if a procedure expects an integer as a parameter the compiler checks that an
integer is being presented to it.
In Smalltalk, neither the structure of the objects is fixed nor are the actual types of parameters etc.
likely to be known. It is therefore necessary to perform object integration testing in a methodological
and principled manner. If the specification of two classes indicates that they are intended to collaborate
to achieve some behavior, then those two classes should be tested together. Again the specification
should be used to generate scenarios which exercise normal and abnormal interactions. These scenarios
can then be used to define tests to perform. Having tested the two classes other cooperations may be
identified involving these and other classes. Each of these collaborations also needs to be tested.
Integration testing (like multiple method testing in a single class) relies on the identification of
scenarios which will be used to define appropriate test suites. However, consideration should also be
given to identifying anticipated message paths. The differences b etween these two tests are akin to
black box and white box testing for a single method. The scenario based testing relies on testing the
specification of the behavior of the collaborating objects, while the white box testing is intended to test
particular message paths through the classes. Again, the two approaches to testing are intended to be
used together.
23.3 System testing
System testing of Smalltalk systems should be carried out in essentially the same way as system testing
of any computer system. This is because a system implemented in Smalltalk should be subject to the
same types of requirements as a system written in any other language. There are some special situations
which you might wish to test for, such as ensuring that the system does not run out of memory before a
garbage collection is forced or that the system will still work once the image has been “stripped” of
those classes not required by the production system (e.g. the compiler classes etc.). However, in general
the system should be subject to the same range of tests as any other.
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