4.3.3 The Value of Statement and Decision Testing

When 100% statement coverage is achieved, it ensures that all executable statements in the code have been tested at least once, but it does not ensure that all decision logic has been tested. Of the two whitebox techniques discussed in this syllabus, statement testing may provide less coverage than decision testing.

When 100% decision coverage is achieved, it executes all decision outcomes, which includes testing the true outcome and also the false outcome, even when there is no explicit false statement (e.g., in the case of an IF statement without an else in the code). Statement coverage helps to find defects in code that was not exercised by other tests. Decision coverage helps to find defects in code where other tests have not taken both true and false outcomes.

Achieving 100% decision coverage guarantees 100% statement coverage (but not vice versa).