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+1

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+To give you a slightly better understanding of the differences

+

+2

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+between black-box testing and white-box testing, I am going to provide you

+

+3

+00:00:06,300 --> 00:00:10,040

+a couple of simple examples that illustrate the, the strengths and

+

+4

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+limitations of these two techniques. So, in this case, let's start

+

+5

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+with black-box testing, so we're only working with this specification.

+

+6

+00:00:15,750 --> 00:00:18,540

+So, let's say that our specification says that this is a

+

+7

+00:00:18,540 --> 00:00:23,550

+program that inputs an integer value and prints it. And implementation,

+

+8

+00:00:23,550 --> 00:00:25,900

+we don't know because we're working at the black box level.

+

+9

+00:00:25,900 --> 00:00:28,710

+If we wanted to test this function according to its

+

+10

+00:00:28,710 --> 00:00:32,060

+specification, what we will probably do is to select a positive

+

+11

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+integer, a negative integer, and the zero as test inputs

+

+12

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+and see how the program behaves for these inputs. So let

+

+13

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+me now show you a possible implementation for this specification.

+

+14

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+What I'm showing here is this function that we called print

+

+15

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+NumBytes, which takes the parameter and prints it. And one thing

+

+16

+00:00:48,010 --> 00:00:50,905

+that we notice right away is that, although in the specification,

+

+17

+00:00:50,905 --> 00:00:53,960

+numbers that are less than 1024 and numbers that

+

+18

+00:00:53,960 --> 00:00:57,320

+are greater or equal to 1024 are exactly equivalent from

+

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+the specification standpoint. They're however treated differently in the

+

+20

+00:01:01,020 --> 00:01:04,140

+code, so the developer decided that the program was just

+

+21

+00:01:04,140 --> 00:01:06,200

+going to print the value of the parameter if it's

+

+22

+00:01:06,200 --> 00:01:09,300

+less than 1024. But it was actually divided by 1024

+

+23

+00:01:09,300 --> 00:01:13,560

+and printing it with a kilobyte mark after it

+

+24

+00:01:13,560 --> 00:01:16,170

+if you are greater than 1024. And notice that here,

+

+25

+00:01:16,170 --> 00:01:19,370

+there is a problem. The developer, just a number 124, instead

+

+26

+00:01:19,370 --> 00:01:22,840

+of 1024. So there's probably a typo in this point in the

+

+27

+00:01:22,840 --> 00:01:26,260

+code. So this is a case in which by simply doing black-box

+

+28

+00:01:26,260 --> 00:01:28,750

+testing, so by simply looking at the specific issue, we might miss

+

+29

+00:01:28,750 --> 00:01:31,510

+this problem. Because we have no reason to consider numbers that are

+

+30

+00:01:31,510 --> 00:01:34,780

+less than 1024 or greater than 1024. However if we were to

+

+31

+00:01:34,780 --> 00:01:38,010

+look at the code, so operating at white-box manner, we will right

+

+32

+00:01:38,010 --> 00:01:41,340

+away see that we need to have a test case that checks

+

+33

+00:01:41,340 --> 00:01:44,880

+the program when the parameter is greater than 1024. And we will find

+

+34

+00:01:44,880 --> 00:01:47,300

+the problem right away. So now let me show you a dual example.