Test-Driven Development

Test-Driven Development

1. Why?

   • $607b in 2020 for bugs in US
   • Cost 100x in maintenance phase
   • incremental specification
   • developer discipline
   • regression errors

2. How?

   • Verification
     • Dynamic Verification (Testing)
       • Try to make system fail
       • Executing in runtime environment for expected behavior
       • Testing levels: unit, integration, system, acceptance, regression
       • Stages
         • Outside org
           • Beta, product release
         • Within org
           • developers', alpha
       • Techniques
         • opaque box
         • clear box
     • Static Verification
       • Examine w/o executing
       • Performed asap
       • DNR runtime env or compilation
     • Inspections/Reviews/Walkthroughs
       • Human-intensive
       • Group-based, manual
       • formal checklist + moderator, less formal + peers, informal + author
     • Formal Verification
       • math exhaustive
       • checks code response to situation
       • time consuming + expensive

3. What?

   • test written before class
   • write test code, functional code, refactor
     • Refactoring
       • What?
         • Improve design
         • Preserve functionality
       • Why?
         • Requirements change
         • Improve design
         • programmer sloppiness
         • flexibility
       • Types
         • Collapse heirarchy
         • Extract method
         • Consolidate conditional
         • Decompose conditional
         • Extract class
       • When?
         • Adding a feature
         • code review
         • fixing a bug
         • not when code is broken
         • not close to deadline
         • not without reason
       • Tools
         • Built into many IDEs
       • How to find problem?
         • Code Smells
           • What?
             • quick to spot
             • indication of bigger problem
           • From Where?
             • rushed design
             • technical debt
               • right way vs fast way
           • Types
             • Bloaters
               • Large class
               • Long method
               • Data clumps
               • Long param list
             • OO Abusers
               • Switch statements
               • Refused bequest
             • Change Preventers
               • Shotgun surgery
               • Divergent change
             • Dispensables
               • Duplicated code
               • Lazy class
               • Data class
             • Couplers
               • Feature envy
               • Inapprorpiate Intimacy
               • Middleman
   • Red, green, refactor
     • make it fail, make it work, make it better