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The next type of software process models that I

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want to discuss are Agile Software Development Processes. And this

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is a group of software development methods that are

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based on highly iterative and incremental development. And in particular,

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I'm going to discuss Test Driven Development or TDD. The

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space on the iteration of three main phases. In

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the first one that we mark as red, we

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write test cases that encode our requirements, and for which

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we haven't written code yet. And therefore, they will fail, obviously.

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So we're in this sort of red or fail phase. From

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this phase, we move to this phase, in which after we

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write the just enough code to make the test cases pass.

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We have a set of test cases that are all passing.

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And therefore, we can consider this as the green phase. We

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had enough code to make the test cases pass because the

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test cases encode our requirements. We have just written enough code to

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satisfy our requirements. When we do this over time though,

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what happens is that the structure of the code deteriorates, because

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we keep adding pieces. So that's why we have the

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first step, which is refactoring. In this step, we modify the

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code, and we will talk about refactoring extensively. We'll devote

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one lesson to it. We modify the code to make it

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more readable, more maintainable. In general, we modify to improve the

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design of the code. And after this phase, we will go

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back to writing more test cases for

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new requirements, write code that makes these

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test cases pass, and so on. So we'll continue to iterate among these phases. And

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also, in this case, we will talk

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about Agile Software Processes. And in particular,

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about extreme programming, or XP, and Scrum

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in more details, in minor course number four.