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+1
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+Something that we saw when we were looking at the split
+
+2
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+program before is that if we just combine the interesting values that
+
+3
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+we identify, we might end up with a lot of cases.
+
+4
+00:00:08,490 --> 00:00:11,030
+And I mentioned that we, we're going to look at some way of
+
+5
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+addressing that problem. And this is exactly what happens in the
+
+6
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+next step of the category partition method, in which we identify constraints
+
+7
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+among choices. And why do we identify these constraints? We do
+
+8
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+that to eliminate meaningless combinations of
+
+9
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+inputs. If you remember, for example,
+
+10
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+we had the case in which we were trying to
+
+11
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+create a string with a size less than 0, which
+
+12
+00:00:30,110 --> 00:00:32,930
+doesn't make any sense. And very importantly, we also do
+
+13
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+that to reduce the number of test cases. Because every time
+
+14
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+we constrain one of the possible choices, we eliminate possible
+
+15
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+test cases, so we can use it to keep under
+
+16
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+control the number of tests that we generate. There are
+
+17
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+three types of properties. The
+
+18
+00:00:47,571 --> 00:00:50,610
+pair property...if, error properties, and properties
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+19
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+of type single. So we're going to look at what these
+
+20
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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
+
+22
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+identified earlier. So let's look, for example, at choice 0, for
+
+23
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+category length of the string. All we can say is that,
+
+24
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+if the length is 0, this define a special property of
+
+25
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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
+
+32
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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.
+
+37
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+So, if zerovalue is not defined. So this pair is an
+
+38
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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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+00:01:56,480 --> 00:01:59,510
+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
+
+44
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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
+
+46
+00:02:09,949 --> 00:02:12,990
+once because we assume that we just want to test this error condition
+
+47
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+once. Finally, the single property is a property that we use
+
+48
+00:02:16,260 --> 00:02:19,050
+when we want to limit the number of test cases. And it's
+
+49
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+similar as an effect to error. It just has a different
+
+50
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+meaning. So what we do when we use the single property is
+
+51
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+that we're saying that this choice, we want to use in only
+
+52
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+one combination. So don't combine it multiple times. And that, of course,
+
+53
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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
+
+55
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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
+
+57
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+equal to maxint. We're actually going to see a demo
+
+58
+00:02:44,300 --> 00:02:46,880
+on this topic so we'll have more chances of seeing how
+
+59
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+properties work in practice and how good they are at
+
+60
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+eliminating meaningless combinations and at reducing the number of test cases.