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| <mainDescription><h3>
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| Introduction
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| </h3>
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| <p>
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| With Test-First Design (TFD) you do detailed design in a just-in-time (JIT) manner via writing a single test before
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| writing just enough production code to fulfill that test. When you have new functionality to add to your system,
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| perform the following steps:
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| </p>
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| <ol>
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| <li>
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| <strong>Quickly add a developer test</strong>. You need just enough implementation code to fail.&nbsp; For example,
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| a new method about to be added to a class could be created that just throws a fatal exception.
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| </li>
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| <li>
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| <strong>Run your tests</strong>. You will typically run the complete test suite, although for sake of speed you may
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| decide to run only a subset. The goal is to ensure that the new test does in fact fail.
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| </li>
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| <li>
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| <strong>Update your production code</strong>. The goal is to add just enough functionality so that&nbsp;the code
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| passes the new test.&nbsp;
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| </li>
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| <li>
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| <strong>Run your test suite again</strong>. If they tests fail you need to update your functional code and retest.
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| Once the tests pass, start over.
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| </li>
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| </ol><br />
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| <p>
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| <img height="600" alt="Test First Design Flow" src="./resources/test_first_design.jpg" width="294" />
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| </p>
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| <h4>
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| Why TFD?
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| </h4>
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| <p>
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| A significant advantage of TFD is that it enables you to take small steps when writing software, which is not only
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| safer it is also far more productive than writing code in large steps. For example, assume you add some new functional
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| code, compile, and test it. Chances are pretty good that your tests will be broken by defects that exist in the new
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| code. It is much easier to find, and then fix, those defects if you've written five new lines of code than fifty lines.
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| The implication is that the faster your compiler and regression test suite, the more attractive it is to proceed in
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| smaller and smaller steps.
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| </p>
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| <p>
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| There are other other common testing strategies (listed here in order of effectiveness).
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| </p>
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| <ol>
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| <li>
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| <strong>Write several tests first</strong>. This is a variant of TFD where you write more than one test before
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| writing just enough production code to fulfill those tests. The advantage is that you don't need to build your
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| system as often, potentially saving time. It has the disadvantage that you will write more production code at once,
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| increasing the difficulty of finding the cause of new bugs.
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| </li>
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| <li>
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| <strong>Test after the fact</strong>. With this approach you write some production code then you write enough
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| testing code to validate it. This has the advantage that you're at least still validating the code but has the
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| disadvantage that you lose the design benefit inherent in writing the testing code first.
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| </li>
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| </ol><br />
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| <h3>
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| Good Things to Know
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| </h3>
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| <p>
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| 1. An underlying assumption of TFD is that a unit-testing framework is available. Agile software developers often use
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| the xUnit family of open source tools, such as <a href="http://www.junit.org/"><strong>JUnit</strong></a> or <a
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| href="http://www.vbunit.org/"><strong>VBUnit</strong></a>, although commercial tools are also viable options.
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| </p>
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| <p>
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| 2. Test-Driven Design (TDD) = TFD + <a class="elementLink" href="./../../../openup/guidances/concepts/refactoring.html"
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| guid="_Poc7IPDzEdqYgerqi84oCA">Refactoring</a>
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| </p>
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| <p>
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| 3. TFD/TDD is commonly used with object-oriented business code, although this approach can be taken with procedural
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| code, user-interface code, and database code.
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| </p></mainDescription> |
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