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Something that we saw when we were looking at the split
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program before is that if we just combine the interesting values that
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we identify, we might end up with a lot of cases.
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And I mentioned that we, we're going to look at some way of
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addressing that problem. And this is exactly what happens in the
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next step of the category partition method, in which we identify constraints
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among choices. And why do we identify these constraints? We do
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that to eliminate meaningless combinations of
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inputs. If you remember, for example,
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we had the case in which we were trying to
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create a string with a size less than 0, which
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doesn't make any sense. And very importantly, we also do
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that to reduce the number of test cases. Because every time
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we constrain one of the possible choices, we eliminate possible
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test cases, so we can use it to keep under
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control the number of tests that we generate. There are
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three types of properties. The
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pair property...if, error properties, and properties
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of type single. So we're going to look at what these
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properties mean, using, once more, our example of the split program.
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In particular, we're going to use some of the choices that we
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identified earlier. So let's look, for example, at choice 0, for
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category length of the string. All we can say is that,
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if the length is 0, this define a special property of
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the string. And that was specified in this way by saying
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that this identifies property zerovalue. So every time that we use
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this choice, zerovalue is defined. At this point, we can use
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this to exclude some meaningless
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combinations. For instance, consider special characters.
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If we have a string of length 0, which means a
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string with no characters. Obviously, there
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cannot be special characters. So, considering
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this combination will just be a waste of time. So what
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we do is that we specify next to this choice, that we
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will only consider this if length is not 0. And we
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do this by saying that we consider this only if not zerovalue.
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So, if zerovalue is not defined. So this pair is an
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example of a property...if case. Define a property and use that
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property. Now let's look at a case in which we might
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want to use an error property. For instance, when we look at
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the category value for the input size, the choice value less
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than 0 is an erroneous choice. So it's a choice that
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we selected to test a possibly erroneous situation, so we can
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mark this as an error property. And what that means is that
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when generating a combination of choices, we will consider this only
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once because we assume that we just want to test this error condition
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once. Finally, the single property is a property that we use
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when we want to limit the number of test cases. And it's
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similar as an effect to error. It just has a different
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meaning. So what we do when we use the single property is
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that we're saying that this choice, we want to use in only
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one combination. So don't combine it multiple times. And that, of course,
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given the combinatorial nature of the problem, cuts down dramatically
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the number of test cases. And we might use, for
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instance, the single property for maxint, which means that we
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will only have one test case in which the size is
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equal to maxint. We're actually going to see a demo
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on this topic so we'll have more chances of seeing how
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properties work in practice and how good they are at
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eliminating meaningless combinations and at reducing the number of test cases.
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