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2.2 How Do We Test?
There are many techniques for testing. Some can be applied to more than one test phase. None ensures
bug-free software: each has its own strengths, limitations, and costs.
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Functional
(black-box) methods can be applied to any unit, build, or system, since they assume
no knowledge of how either was constructed or what it contains. Such methods require a sufficient
and unambiguous specification if they are to be effective. (Devising black-box tests for some code
from its specification at the time the specification is written is a useful verification of the speci-
fication; if it can??™t be done, the specification isn??™t good enough.) This is what you will normally
do for a system test.
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Structural
(white-box) methods can also be used on any unit or build, but are cheapest to devise
when used on structured programs, e.g., well-written programs in a structured language. These
are usually applied to unit tests.
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Dynamic analysis
techniques are derivative methods which assume that a particular technique
such as condition tables, finite state machines, object-orientation, or functional programming,
has been used to develop the software; we use knowledge of that technique to determine the
test
cases,
so these have very special areas of application. These can be applied at both system test and
unit test times. These are usually applied to unit tests.
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Static analysis
techniques can best be used before integration, and can also point to the need for
more-rigorous unit testing.
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