Test Driven Development

Transcript

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