ESA PSS-05-10 Issue 1 Revision 1 (March 1995) 27
SOFTWARE VERIFICATION AND VALIDATION
Equivalence classes may be defined by considering all possible
data types. For example the module above accepts integers only. Test
cases could be devised using real, logical and character data.
Having defined the equivalence classes, the next step is to select
suitable input values from each equivalence class. Input values close to the
boundary values are normally selected because they are usually more
effective in causing test failures (e.g. 11 might be expected to be more likely
to produce a test failure than 99).
Although equivalence partitioning combined with boundary-value
selection is a useful technique for generating efficient input data sets, it will
not expose bugs linked to combinations of input data values. Techniques
such as decision tables [Ref 12] and cause-effect graphs [Ref 14] can be
very useful for defining tests that will expose such bugs.