Well-behaved objects - Objects First with Java: A Practical Introduction Using BlueJ - page 237

In this chapter, we shall discuss a variety of activities that are related to improving the correct-
ness of a program. These include testing, debugging, and writing for maintainability.

Testing is an activity that is concerned with finding out whether a segment of code contains any
errors. Testing well is not easy, and there is much to think about when testing a program.

Concept:

Testing is the ac-
tivity of finding out
whether a piece of
code (a method,
class, or program)
produces the in-
tended behavior.

Debugging comes after testing. If tests have shown that an error is present, we use debugging
techniques to find out exactly where the error is and how to fix it. There can be a significant
amount of work between knowing that an error exists and finding the cause and fixing it.

Writing for maintainability is maybe the most fundamental topic. It is about trying to write code
in such a way that errors are avoided in the first place and, if they still slip in, that they can be
found as easily as possible. Code style and commenting are part of it, as are the code quality
principles that we have discussed in the previous chapter. Ideally, code should be easy to under-
stand so that the original programmer avoids introducing errors and a maintenance programmer
can easily find possible errors.

Concept:

Debugging is the
attempt to pinpoint
and fix the source
of an error.

In practice, this is not always simple. But there are big differences between few and many errors
and also between the effort it takes to debug well-written code and not-so-well-written code.

7.2 Testing and debugging

Testing and debugging are crucial skills in software development. You will often need to check
your programs for errors and then locate the source of those errors when they occur. In addition,
you might also be responsible for testing other people's programs or modifying them. In the
latter case, the debugging task is closely related to the process of understanding someone else's
code, and there is a lot of overlap in the techniques you might use to do both. In the sections
that follow, we shall investigate the following testing and debugging techniques:

■ manual unit testing within BlueJ
■ test automation
■ manual walkthroughs

■ print statements
■ debuggers
We shall look at the first two testing techniques in the context of some classes that you might
have written for yourself, and the remaining debugging techniques in the context of understand-
ing someone else's source code.

7.3 Unit testing within BlueJ

The term unit testing refers to a test of the individual parts of an application, as opposed to
application testing , which is testing of the complete application. The units being tested can be
of various sizes. They may be a group of classes, a single class, or even a single method. It is
worth observing that unit testing can be done long before an application is complete. Any single
method, once written and compiled, can (and should) be tested.