With TDD, the unit test is written first with a test that fails, you then write the code that will execute and allow the unit test to pass. Overall TDD saves time spent performing unit tests and other similar tests since test creation is developed before the code has even been written.
- Run the test case again confirming test passes (Green)
- Refactor the code as per typical standards (Refactor)
These steps follow the principle of Red-Green-Refactor. The Red-Green steps ensure that you write the simplest code possible to solve the problem while the last step makes sure that the code that you write is up to typical coding standards.
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#### More Information:
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Agile Data's <ahref='http://agiledata.org/essays/tdd.html'target='_blank'rel='nofollow'>Introduction to TDD</a>
Wiki on <ahref='https://en.wikipedia.org/wiki/Test-driven_development'target='_blank'rel='nofollow'>TDD</a>
Martin Fowler <ahref='https://martinfowler.com/articles/is-tdd-dead/'target='_blank'rel='nofollow'>Is TDD Dead?</a>
(A series of recorded conversations on the subject)
Kent Beck's book <ahref='https://www.amazon.com/Test-Driven-Development-Kent-Beck/dp/0321146530'target='_blank'rel='nofollow'>Test Driven Development by Example</a>
Uncle Bob's <ahref='http://blog.cleancoder.com/uncle-bob/2014/12/17/TheCyclesOfTDD.html'target='_blank'rel='nofollow'>The Cycles of TDD</a>