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    <ul> <li>Do you do design up front? </li> </ul> <p>Of course you do. You've got a big application in front of you. You've got to have some idea of the structure it will have before you start writing tests and code. You don't have to have it all worked out in detail, but you should have some basic idea of the layers, components, and interfaces. For example, if you are working on a web services system, you ought to know what the top level services are, and have a good first approximation of their signatures.</p> <ul> <li>Do you write the entire application using nothing but stubbed out code?</li> </ul> <p>No. You stub things out only if they are really difficult to control in a test. For example, I like to stub out the database, and the UI. I will also stub out third party interfaces. Sometimes I will stub out one of my own components if it vastly increases the test time, or it forces me to create test data that is too complicated. But most of the time I let my tests work on a pretty well integrated system.</p> <p>I have to say I really dislike the style of testing that relies heavily on mocks and stubs. Don't get me wrong, I think mocks and stubs are very useful for decoupling from things that are hard to test. But I don't like writing things that are hard to test, and so I don't use a lot of mocks and stubs.</p> <ul> <li>How do you write your first unit test for a high level function?</li> </ul> <p>Most high level functions have degenerate behavior. For example, login is a pretty high level function and can be very complicated. But if you try to log in with no user name and no password, the response from the system is going to be pretty simple. Writing that tests will also be very simple. So you start with the degenerate cases. Once you have exhausted them, you move on to the next level of complexity. For example, what if a user tries to log in with a username but no password? Bit by bit you climb the ladder of complexity, never tackling the more complex aspects until the less complex aspects are all passing.</p> <p>It is remarkable how well this strategy works. You might think that you'd just be climbing around the edges all the time and never getting to the meat; but that's not what happens. Instead you find yourself designing the internal structure of the code based on all the degenerate and exceptional cases. When you finally get around to the primary flow, you find that the structure of the code you are working on has a nice hole of just the right shape to plug the main flow in.</p> <ul> <li>Please don't create your UI first. </li> </ul> <p>UIs are misleading things. They make you focus on the wrong aspects of the system. Instead, imagine that your system must have many different UIs. Some will be web, some will be thick client, some will be pure text. Design your system to work properly irrespective of the UI. Get all the business rules working first, with all tests passing. Then plug the UI in later. I know this flies in the face of a lot of conventional wisdom, but I wouldn't do it any other way.</p> <ul> <li>Please don't design the database first. </li> </ul> <p>Databases are details. Save the details for later. Rather, design your system as though you had no idea what kind of database you were using, Keep any notion of schema, tables, rows, and columns out of the core of the system. Implement your business rules as though all the data were kept in memory all the time. Then add the database later, once you've gotten all the business rules working. Again, I know this flies in the face of some conventional wisdom, but coupling systems to databases too early is a source of a lot of badly warped designs.</p>
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    1. POdesign of mid-large sized application when doing TDD?
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    1. USRobert C. Martin
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    1. COAwesome reply. Thanks again
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      1. USdferraro
    2. CO"Please don't create your UI first". I strongly disagree. Without (static) UI first you may be just coding wrong thing. Another good read: http://www.codinghorror.com/blog/2008/04/ui-first-software-development.html
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      1. USŁukasz Wiatrak
    3. COAnother good answer: http://stackoverflow.com/questions/1554419/when-i-proceed-to-develop-a-software-ui-design-or-database-design-which-should
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