Excel TDD

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Excel _at_ TDD

• An introduction to how to keep software soft
• Karl Scotland

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What if

• Everything worked one minute ago
• A regression test suite naturally evolved with
  the system
• The system was really easy to change
• Developers had examples to help understand code
• The system design was easy to test
• Developers were addicted to having a working
  system

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An example using Excel and VBA

• Convert integers to Roman numerals
• Assume ROMAN() does not exist
• Imagine Im actually in Excel

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i2r(A2)
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i2r
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Shift-F9 runs the tests
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IF(B2C2, Pass, Fail)
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i, ii, iii pattern
Repeated here
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What Just Happened

• Took baby steps
• Red ? Green ? Refactor
• Hard coded values (Fake it till you Make it)
• Evolved the design
• Expected failures
• Found typo almost immediately
• Used Excel and VBA

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What if

• Everything worked one minute ago
• A regression test suite naturally evolved with
  the system
• The system was really easy to change
• Developers had examples to help understand code
• The systems design was easy to test
• Developers were addicted to having a working
  system

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Objections

• What would make TDD difficult?

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Objections

• We dont have time
• We have legacy code
• We have GUIs
• We have Databases
• TDD wont find bugs
• What about QA?
• We wont do it

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My Experience

• TDD
• does not add time
• saves time
• produces high quality design and code
• supports iterative, incremental development
• is fun and addictive

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Next steps

• Test-Driven Development by Example Kent Beck
  (Addison Wesley 2002)
• JUnit, phpUnit etc.
• http//www.testdriven.com
• Ping me (kjscotland)
• Try it!

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Questions?