(Test Driven) Software Development

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(Test Driven) Software Development

• Erik Zeitler

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Dream up a business case

• Think of a service you want to see
• Figure out how to do it in a way that doesnt
  suck
• Do it

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How to do it?

• Think about the use cases
• How will the service be used
• Cut the work into pieces
• User Interface, application code, database
• Assign pieces within the project group
• Use Test Driven Development
• Test each piece (unit tests)
• Test all pieces together (integration/regression
  tests)

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Rapid prototyping

• Make a simple prototype ASAP
• See what new ideas it gives you
• Often, users dont know what they want until
  they see it Steve Jobs
• Show your prototype to the other project groups
• Give feedback to each other

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Three-tier architecture

• User Interface
• What should the user see?
• Make drawings
• Database
• What information will you keep?
• Do data modelling, using ER diagrams
• Business logic
• How will you present the data to the users?
• For any non-trivial function, do test driven
  development

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Data modelling

• Keep persistent data in a database
• Customer information
• Banking information
• Inventory
• What do you carry, and how much do you have right
  now?
• Past activity
• What has the customer bought?
• What has the customer looked at?
• What information do you want to store? Why?
• Make an Entity Relationship diagram
• Translate the ER diagram into SQL tables

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Example of an ER diagram
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Why ER diagrams?

• Keep talking about the algorithms, and everyone
  will stay totally mystified
• Show the ER diagram, and everything else will be
  obvious

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Software development is all about Getting Things
Done

• Priorities in software development
• Make it work
• Make it beautiful
• Make it fast

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How?

• How to make it work?
• First write tests,
• then write code.
• This is called Test Driven Development.
• How to make it beautiful?
• Re-factor
• How to make it fast?
• Dont worry about performance until performance
  is a problem.

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Why TDD?

• Because
• Debugging sucks
• Testing rocks
• Because does it
• A test is a specification
• The capabilities of a program is defined by its
  tests
• If the tests pass
• we know that the program works for the test
  cases.
• A test is a piece of documentation

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The rules of TDD are simple

• You can't write production code unless there is a
  broken test.
• First write a test, then write the code
• When there is a broken test, you change your code
  to make it pass.
• When your code is working, you refactor to
  eliminate any code smells

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What is code smell?

• Something is fishy about the code
• http//en.wikipedia.org/wiki/Code_smell
• Examples
• Large method
• A function that is gt 1 page
• Duplicated method
• A method, function, or procedure that is very
  similar to another.
• Contrived Complexity
• Forced usage of overly complicated design
  patterns where simpler design would suffice

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Demonstration

• yay

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A good set of tests

• Covers all code
• How many lines of code do you have?
• How many lines are tested?
• Do you have gt 90 test coverage?
• performs tests on different scale
• unit integration regression
• tests for all cases, including edge cases and
  errors
• e.g. expectException()

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Different sized tests
Large (regression)
Medium (integration)
Small (unit)
isolation,speed
confidence in whole system
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Where is the bug?
vs.
Test failed
Test failed
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Does the entire system work?

vs.



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Tests for edge cases and errors

• Write tests for invalid input data, like
• empty strings
• empty data sets
• false
• broken input data
• what happens to your functions if they get
  a76tr4234, when they expected a single
  character (e.g. a)?
• Generate exceptions in production code
• catch exceptions in test code

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Test your database

• Set up a test database, identical to your
  production database
• Grant privileges to your php test script
• Call your stored procedures from your php test
  script
• Validate the result data from the database

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Further resources

• Soon available on the course home page
• The latest PHPUnit (simpletest)
• These slides
• My demonstration examples
• IDEs (Eclipse, Netbeans, ...) have infrastructure
  for testing