Test Driven Development

Test Driven Development


Jason Ragsdale

September 08, 2009


  1. TEST DRIVEN DEVELOPMENT DPUG - 09/08/2009 - Jason Ragsdale 1

    Tuesday, September 8, 2009
  2. What is TDD? Test-driven development (TDD) is a software development

    technique that relies on the repetition of a very short development cycle: 1. First write a failing automated test case that defines a desired improvement or new function 2. Then produce code to pass that test 3. Finally refactor the new code to acceptable standards. 2 Tuesday, September 8, 2009
  3. The Three Laws of TDD 1. Don’t write any code

    unless it is to make a failing test pass. 2. Don’t write any more of a unit test than is sufficient to fail. 3. Don’t write more code than is sufficient to pass the one failing unit test. 3 Tuesday, September 8, 2009
  4. The Development Cycle 4 Tuesday, September 8, 2009

  5. Benefits The first goal is to make the test pass.

    Subsequent users have a greater level of trust in the code. Executable Documentation. 5 Tuesday, September 8, 2009
  6. Limitations Some Code is Hard to Test. Don’t Test That

    Code, Minimize that Code. Put the important code in a library and test that code. 6 Tuesday, September 8, 2009
  7. Limitations Management support is essential. Without the organization support, that

    TDD is going to improve the product. Management will feel that time spent writing tests is wasted. 7 Tuesday, September 8, 2009
  8. Limitations Badly written tests, are expensive to maintain. 8 Tuesday,

    September 8, 2009
  9. Limitations The level of coverage and testing detail achieved during

    repeated TDD cycles cannot easily be re-created at a later date. Therefore these original tests become increasingly precious as time goes by. If a poor architecture, a poor design or a poor testing strategy leads to a late change that makes dozens of existing tests fail, it is important that they are individually fixed. Merely deleting, disabling or rashly altering them can lead to un- detectable holes in the test coverage. 9 Tuesday, September 8, 2009
  10. Limitations Unexpected gaps in test coverage may exist or occur

    for a number of reasons. One or more developers in a team was not so committed to the TDD strategy and did not write tests properly. Some sets of tests have been invalidated, deleted or disabled accidentally or on purpose during later work. Alterations may be made that result in no test failures when in fact bugs are being introduced and remaining undetected. 10 Tuesday, September 8, 2009
  11. Limitations Unit tests created in a TDD environment are typically

    created by the developer who will also write the code that is being tested. The tests may therefore share the same blind spots with the code. 11 Tuesday, September 8, 2009
  12. Limitations The high number of passing unit tests may bring

    a false sense of security 12 Tuesday, September 8, 2009
  13. Unit Tests A unit is the smallest testable part of

    an application. 13 Tuesday, September 8, 2009
  14. Unit Tests 1 <?php 2 class WhenTestingAdder { 3 public

    function shouldAddValues() { 4 $adder = new Adder(); 5 $this->assertEquals(2, $adder->add(1, 1)); 6 $this->assertEquals(3, $adder->add(1, 2)); 7 $this->assertEquals(4, $adder->add(2, 2)); 8 $this->assertEquals(0, $adder->add(0, 0)); 9 $this->assertEquals(-3, $adder->add(-1, -2)); 10 $this->assertEquals(0, $adder->add(-1, 1)); 11 $this->assertEquals(2222, $adder->add(1234, 988)); 12 } 13 } 14 ?> 14 Tuesday, September 8, 2009
  15. Integration Tests Individual software modules are combined and tested as

    a group. It occurs after unit testing and before system testing. 15 Tuesday, September 8, 2009
  16. System Tests Testing conducted on a complete, integrated system to

    evaluate the system’s compliance with its specified requirements. Falls within the scope of black box testing, and as such, should require no knowledge of the inner design of the code or logic. 16 Tuesday, September 8, 2009
  17. Ok Now What? No enhancements without defined requirements. Can not

    write tests for items without requirements. 17 Tuesday, September 8, 2009
  18. Examples HelloWorld TicTacToe 18 Tuesday, September 8, 2009

  19. Q&A 19 Tuesday, September 8, 2009

  20. Links PHPUnit http://www.phpunit.de/ Three Rules of TDD http://butunclebob.com/ArticleS.UncleBob.TheThreeRulesOfTdd TDD -

    Wikipedia http://en.wikipedia.org/wiki/Test-driven_development BDD - Wikipedia http://en.wikipedia.org/wiki/Behavior_Driven_Development http://www.phpspec.org/ 20 Tuesday, September 8, 2009