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In the last lesson, we talked about black-box testing or functional testing,

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which is the kind of testing that you perform when you just

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look at the description of the software. Today we're going to cover white-box

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testing, which is the kind of testing that we perform when we

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open up the box. We look inside the program, and we actually

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test it based on its code. And there is one basic assumption

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behind the idea of white-box testing, which is a very intuitive one,

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and the assumption is that executing the faulty statement is a necessary

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condition for revealing a fault. In other words, if there is

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a bug in the program there is no way were going to be

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able to find this bug or this fault, if we don't execute

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the statement that contains it. Which makes a lot of sense. As

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we did for black-box testing, we're going to start by summarizing what

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are the main advantages of white-box testing. The main advantage is that

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it's based on the code, and as such, the quality of white-box

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testing can be measured objectively. And what I mean here by objectively

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is that if you think about black-box testing In many

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cases, there were subjective decisions, there were had to be made

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in order to define tests in a black-box fashion. In the

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case of white-box testing, because everything is based on the quota,

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we don't have to make such subjective decisions. And similarly, because

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white-box testing is based on the code, it can be measured

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automatically. So we can build tools and actually there are tools,

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and there's plenty of tools, that can be measured, the level

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of white-box testing can be achieved in a fully automated way.

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And we're going to see some of them in the course of the

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class. Another advantage of white-box testing is that it can be

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used to compare test suites. So if you have two alternative sets

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of tests that you can use to assess the quality of

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your software, white-box testing techniques can tell you which one of these

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two test suites is likely to be more effective in testing

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your code. And finally, white-box testing allows for covering the coded behavior

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of the software. What that means is that if there is

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some mistake in the code and is not obvious by looking at

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the specification of the code, white box testing might be able

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to catch it, because it tries to exercise the code. There's many

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different kinds of white box testing, there are control flow based

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techniques, data flow based techniques, and fault based techniques. And for each

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one of these family of techniques there are many variations. So

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this field is very, very broad. In this lesson we will talk

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about white-box testing by focusing

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mainly on control-flow based testing techniques.