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Let's go back to our test criteria subsumption representation, where
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we already had branch coverage and statement coverage. In this case,
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if we want to add condition coverage to this page, we
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have to put it here on this side, with no relationship
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of subsumption with either branch coverage or statement coverage, which
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means that the criteria are not comparable. So now let's consider
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again our last example, and let's use a different test
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with this time. We still have two tests, but the first
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one has x is equal to 0 and y is equal to minus
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5. And the second one, x is equal to 5 and y is
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equal to 5 as well. Let's see what happens in terms of condition
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coverage, when we run these tests. If we look at the first condition, x
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is equal to 0. It is both true, for the first test case,
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and false for the second one. As for the second condition, y greater
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than 0, it is false for the first test case and true for
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the second one. Therefore we've achieved a
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100% condition coverage with these two tests.
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But what about branch coverage? If we consider the whole predicate,
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instead of just the individual conditions, let's see what happens for the
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two test cases. If we look at the first one, because
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x is equal to 0, the overall predicate is true. As for
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the second one, because the second condition is true, the overall
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predicate is true. In other words, despite the fact that we're exercising
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all the possible values for the two conditions, the overall predicate is
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always true. And therefore, we're covering only one of the two branches.
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So our coverage will be 50%. This is the reason
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why normally the two criteria that we just saw, decision
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coverage, and condition coverage are considered together. And the resulting
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criterion is called branch and condition coverage, or also decision
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and condition coverage. At this point the test requirements and
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the coverage measure should be pretty straight forward, because they're
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just considering the two criteria together. As far as the
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requirements are concerned, they include
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all the branches and individual conditions
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in the program. Where as the coverage measure is computed
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considering both coverage measures, both branch coverage and condition coverage.
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