TestDriven Development TDD in PHP

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Test-DrivenDevelopment (TDD)in PHP

• Andre John Cruz
• http//devpinoy.org/blogs/cruizer

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Test-Driven Development

• Write tests before code
• Design methodology, not a test methodology
• Unit tests
• Integration tests

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Why TDD?

• Repeatable, easy-to-run tests
• The concept of context
• Helps you design well-factored classes
• Single responsibility principle
• Predictable code
• Test harness
• Easy refactoring of code
• Automated tests

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The problem with context

• Need to reproduce exactly the same environment
• Need to reproduce exactly the same
  sequence/situation
• Dependencies!
• browser
• database
• sessions and cookies
• and many more...argh! P

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TDD and PHP

• PHP typelessness is great but...
• TDD helps ensure predictability
• Would you want to discover that error during
  development, or during production? )?
• Reduces risks
• Here's an example...

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Run me and find out...

• lt?php
• a 0.7
• b 0.1
• c a b
• if (c 0.8)
• echo "It's correct!\n"
• else
• echo "It's incorrect. c is not equal to 0.8\n"
• ?gt

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Why?!!!

• Floating-point round off errors
• These are errors that are so easy to overlook,
  yet can wreak havoc on your production system
• TDD helps catch these errors by letting you run
  parts of your system in isolation

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Sample in TDD

• lt?php
• require_once '../simpletest/unit_tester.php'
• require_once '../simpletest/reporter.php'
• class SimpleExample extends UnitTestCase
• function testAddition()
• a 0.7
• b 0.1
• c a b
• this-gtassertEqual(c, 0.8)
• test new SimpleExample()
• test-gtrun(new HtmlReporter())
• ?gt

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TDD Frameworks for PHP

• PHPUnit
• SimpleTest
• supports both PHP4 and PHP5
• I like running my tests in the web browser
  because it's colored P

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Skeleton for SimpleTest

• extend the UnitTestCase class
• verify expected values and results using the
  assert methods
• this is called state testing

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Red-Green-Refactor

• TDD prescribes the following steps
• Write a new test FIRST, resulting in a failing
  program (red)?
• Write code to pass the test (green)?
• Remove redundancies and refactor the code as
  necessary
• repeat )?

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Test before code?!

• Intentional programming
• Ensures that your code is designed to be testable
  in chunks
• Ensures that your code doesn't have non-tested
  parts
• Ensures that you feel first-hand how it is to use
  your code )?

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Demo 1

• Password complexity checker
• Takes in a password string as input
• Optional input minimum required characters
• Output whether password is acceptable or not

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Ways to test

• We've looked at state testing already
• Let's look at interaction testing

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Interaction Testing

• Verifies that the class under test is interacting
  with other classes in expected ways
• Helpful in testing functionality with external
  dependencies
• network connections/services
• database
• browser
• files

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Mock Objects

• Substitute objects that appear the same but
  actually just observe things
• Similar to stand-ins used in the movie industry
  )?
• Allow you to remove external dependencies while
  testing units
• Can help you verify that certain methods are
  actually called with correct parameters

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Demo 2

• Let's use a mock object to test email sending
  functionality
• SimpleTest has mocking facilities that we can use
  for this
• Scenario we need to email users whose disk quota
  are 90 utilized.

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Observations

• Mindset pretend that your objects are actors and
  that you tell them what to do (pass a message)?
• State testing is easier than interaction testing
• Test small before testing big
• It seems to take longer to do things the TDD way
  than to go straight to the code
• Did we use a debugger? )?

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TDD Gotchas

• TDD does not lead to bug-free code
• TDD does not mean you do not need QA anymore
• TDD is mainly about design, not testing
• some say it's more appropriate to call it
  Behavior Driven Design
• Use mock objects for quick testing but use the
  real objects for integration testing

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TDD Pointers

• Write the test before writing the code
• Test small
• Stub out external dependencies into mock objects
• How quickly do your tests run?
• Separate unit tests from integration tests

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Thank You!

• Links
• http//devpinoy.org/blogs/cruizer
• http//www.agilealliance.org
• http//www.lastcraft.com
• http//www.phpunit.de
• http//www.phpugph.com