Lecture Notes in Computer Science 3472

298 Christophe Gaston and Dirk Seifert
not ensure test suites which cover all different outcomes of a condition involved
in a given decision. For example, the fact that B is failure causing could remain
undetected with this criterion. To overcome this weakness, three refined criteria
have been introduced.
The condition coverage criterion requires that each possible outcome of
every condition in each decision is produced at least once. To give an example,
we consider again decision D. The condition coverage criterion requires that A
and B have taken all possible outcomes. Thus, a test suite which contains two
test cases, one such that A is true and B is false and the other one such that A
is false and B is true is sufficient to test decision D.
Even though the condition coverage criterion captures all conditions, it is not
powerful enough to capture coverage of decisions. The test suite described above
for condition D illustrates this fact: It consists of two test cases which both make
(A∧B) evaluate to false. To overcome this weakness one must combine condition
coverage and decision coverage. This is done in decision condition coverage.
The decision condition coverage criterion requires that each possible outcome
of every condition in each decision is produced at least once and that each
possible outcome of every decision in the specification is produced at least once.
For decision D, a test suite which only contains two test cases, one such that
A is true and B is true and the other one such that A is false and B is false, is
sufficient to test decision D with regard to decision condition coverage. Decision
condition coverage is strictly stronger than both decision coverage and condition
coverage in the sense that each test suite which satisfies decision condition
coverage satisfies both decision coverage and condition coverage.
The multiple condition coverage criterion requires that each possible
combination of conditions outcomes in each decision is produced at least once.
Again, we consider decision D, a test suite containing four test cases (A is true
and B is true, A is true and B is false, A is false and B is true and A is false and
B is false) is necessary to test D with regard to multiple condition coverage.
Note that multiple condition coverage requires full search of various combinations
of condition values [VB01]. If the number of conditions in a decision is
equal to n, the number of test cases to satisfy multiple condition coverage grows
up to 2 n . This becomes unmanageable even for relatively moderate values of n.
Decision coverage, condition coverage and decision condition coverage criteria require
less test cases. For example, condition coverage requires two test cases per
condition. If a decision contains n conditions, the criterion requires at maximum
2n test cases. However, a test suite which satisfies one of these three weaker
criteria will not cover all combinations of conditions outcomes. The modified
condition decision coverage criterion provides an intermediate position.
The modified condition decision coverage criterion requires that each
possible outcome of every condition in a decision is produced at least once, each
possible outcome of every decision is produced at least once and that each condition
in a decision has been shown to affect the decision’s outcome independently.
A condition is shown to affect a decision’s outcome independently by varying
that condition while all other possible conditions are fixed.