Test Driven Development

1
Test Driven Development

• Ryan Layer

2
Outline

• Definition
• Development Cycle
• Simple Example
• Benefits and Drawbacks
• Testing Frameworks
• IBM Casestudy

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Test Driven Development (TDD)

• An evolutionary approach to development where you
  must first write a test that fails before you
  write new functional code.
• Differs from traditional develop then test
  (maybe) practices.

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Development Cycle
add a test
Pass
run the test
Development continues
Fail
add functionality
Fail
add a test
Development stops
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Example

• We want to develop a method that, given two
  Integers, returns an Integer that is the sum of
  parameters.

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Example (cont.)

• Test
• Integer i
• new Integer(5)
• Integer j
• new Interger(2)
• Object o sum(i,j)

• Method

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Example (cont.)

• Test
• Integer i
• new Integer(5)
• Integer j
• new Interger(2)
• Object o sum(i,j)

• Method
• public static Object sum(Integer i,
• Integer j)
• return new Object()

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Example (cont.)

• Test
• Integer i
• new Integer(5)
• Integer j
• new Interger(2)
• Object o sum(i,j)
• if (o instanceof
• Integer)
• return true
• else
• return false

• Method
• public static Object sum(Integer i,
• Integer j)
• return new Object()

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Example (cont.)

• Test
• Integer i
• new Integer(5)
• Integer j
• new Interger(2)
• Object o sum(i,j)
• if (o instanceof
• Integer)
• return true
• else
• return false

• Method
• public static Integer sum(Integer i,
• Integer j)
• return new Integer()

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Example (cont.)

• Test
• Integer i
• new Integer(5)
• Integer j
• new Interger(2)
• Object o sum(i,j)
• if ((o instanceof
• Integer)
• ((new Integer(7))
• .equals(o))
• return true
• else
• return false

• Method
• public static Integer sum(Integer i,
• Integer j)
• return new Integer()

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Example (cont.)

• Test
• Integer i
• new Integer(5)
• Integer j
• new Interger(2)
• Object o sum(i,j)
• if ((o instanceof
• Integer)
• ((new Integer(7))
• .equals(o))
• return true
• else
• return false

• Method
• public static Integer sum(Integer i,
• Integer j)
• return new Integer(
• i.intValue()
• j.intValue())

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Benefits

• Reduce gap between decision and feedback
• Encourages developers to write code that is
  easily tested
• Creates a thorough test bed

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Drawbacks

• Time must be taken away from core development
• Some code is difficult to test

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Testing frameworks

• JUnit
• A test structure definition
• Tools to run tests
• A Simple and Practical Approach to Unit Testing
  The JML and JUnit Way by Y. Cheon and G. T.
  Leavens

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Case Study IBM

• IBM Retail Store Solutions (RSS) developing Java
  for Point of Sale (JavaPOS) spec
• For each revision the defect rate was not
  reducing
• Development team chose TDD as a possible solution

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Case Study TDD Concerns

• Defect Rate
• Long term and short term affect
• Productivity
• Lines of code per month impact
• Test Frequency
• Ratio of interactive to automated
• Design
• Design robustness
• Integration
• Smoothness of code integration

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Case Study TDD Results

• Defect Rate
• 50 improvement
• Productivity
• Below initial estimates (
• Test Frequency
• 86 of tests where automated
• Design
• Aided in late changes
• Integration
• Testing made problems surface early

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References and links

• S. Amber. Introduction to Test Driven Development
  (TDD). www.agiledata.org
• E. M. Maximilien and L. Williams. Assessing
  Test-Driven Development at IBM. 25th
  International Conference on Software Engineering,
  2003
• K. Beck and E. Gama. Test infected Programmers
  love writing tests. Java Report, 3(7), July 1998
• Y. Cheon and G. T. Leavens. A Simple and
  Practical Approach to Unit Testing The JML and
  JUnit Way. Report01-12, Dept. of Computer
  Science, Iowa State University, Nov. 2001
• http//www.testdriven.com
• http//www.junit.org

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Questions?