Test Driven Development

Test Driven Development (TDD)
What TDD is and is not
Basics of how to do TDD
Steps
Tools
Where to go to learn more
Can it be used in your projects
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What is it?
A design (not a testing) technique
Formally defined as a practice in 2001
Used in both agile and extreme programming
Best used on new projects with less than a few dozen developers
Can be used to add new features to an existing project that didn’t originally use TDD
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Test Types
Programmer
NOT unit tests
Ideally written in same language as the application
Tool: NUnit or JUnit
Customer
A.k.a. Acceptance or functional tests
Written in a language the customer understands
Tool: FIT – Framework for Integrated Test
Tester Tests
Traditional QA-type tests
Outside scope of TDD
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Basic Rules
Before writing any code, write the test for it first
Implement the feature
Eliminate duplicate code and refine the design
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Basic Rules: Write the Test
Use a tool such as NUnit or JUnit
The test will define the public interface
Focus is on how to use your interface
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Basic Rules: Implement the Feature
Write just enough to satisfy the requirement
Appropriate for the skill level of the one who will be maintaining it
Passes all tests
Communicates intent as clearly as possible
Duplication is allowed
Has the smallest number of classes
Has the smallest number of methods
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Basic Rules: Eliminate Duplicate Code
Eliminate duplicate code and refine the design
Unless it shows the intent of the design more clearly
Avoids inconsistency
Use refactoring
Definition: Improving code without changing its functionality
Complexity can be added if it is done to remove duplication
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Steps
Brainstorm list of tests for a feature
Write them down
Cross them off as they’re implemented
You’re finished when all tests have been crossed off
Perform “Red/Green/Refactor” process
Red/Green refers to test results
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Red/Green/Refactor Process
Choose a test from the list
Write the test code
Compile the test code – this should fail
Implement just enough to compile
Run the test and see it fail
Implement just enough to make the test pass
Run the test and verify it passes
Refactor for clarity and to eliminate duplication
Brainstorm additional tests
Repeat
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Red/Green/Refactor Process
The steps are intentionally very small
Makes it easier to find a mistake
Can speed up development
Less time spent debugging
Confidence in the code that has already been written
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Refactoring
Improving code without changing its functionality
Can be thought of as patterns for changing existing code
Focus is on making existing code cleaner and easier to understand
Examples from “Refactoring” by Martin Fowler
Extract Method
Inline Method
(over 70 more)
Tools available for C#, Java, Visual Basic and a few other languages (see www.refactoring.com)
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Tools: NUnit
Framework for creating automated tests
NUnit is for .NET; JUnit for Java, vbUnit for Visual Basic and CppUnit for C++
Has both GUI and command-line interfaces
Tests can be run by an automated build process
Free
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NUnit Example
Passed tests are green, failures are red and ignored tests are yellow
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NUnit Example
Reference nunit.Framework.dll
Add TestFixture class.
Run using nunit-gui.exe
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Tools: FIT (Framework for Integrated Test)
Framework for creating customer acceptance tests
Uses HTML tables created using MS Word, MS Excel
Customer shows expected results in the table
Developer adds FIT Fixture
FIT updates HTML table to show actual vs. expected results
Has both GUI and command-line interfaces
Free
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FIT Example
Cunningham, Ward. Framework for Integrated Test. September 7, 2002. http://fit.c2.com
Successes and failures are highlighted
Easy for technical and non-technical users to understand
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FIT Example
Cunningham, Ward. Introduction to FIT. Framework for Integrated Test. September 7, 2002. http://fit.c2.com/wiki.cgi?IntroductionToFit
The fixture is fed data from the HTML table
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Summary
TDD is a design technique
Red/Green/Refactor
Tools: NUnit and FIT
Appropriate for your project?
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Where to Get More Information
Online
www.TestDriven.com
www.nunit.org or www.junit.org
nunitforms.sourceforge.net
fit.c2.com
www.refactoring.com
www.sourceforge.net (NUnitForms, NUnitAsp)
Books
“Test-Driven Development in Microsoft .NET”, by James W. Newkirk and Alexei A. Vorontsov (Microsoft Press, 2004)
“Test-Driven Development: By Example”, by Kent Beck (Addison Wesley, 2003)
“Refactoring: Improving the Design of Existing Code”, by Martin Fowler (Addison-Wesley, 1999)
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