2.3 Robust Programs

2.3 Robust Programs

1. DEFENSIVE DESIGN CONSIDERATIONS

   • Input Sanitisation
     • removes unwanted characters of an input before using it as data for next process
       • e.g. changing the case
   • Input Validation
     • checks if data meets certain criteria before processing
       • e.g. checking that an email has a suitable ending .com
     • Types of validation
       • type check
         • range check
           • presence check
             • format check
               • length check

2. PLANNING FOR CONTINGENCIES

   • Communication Error
     • should enable ways for user to cancel requests or report connection errror
       • program can automatically resume when connection is available
   • Peripheral Errors
     • printer may run out of paper, have a jam etc.
       • shouldn't assume printer is always successful
   • Disk Errors
     • e.g. file not found, out of space, corrupt data etc.
       • check files before attempting to use them for processing
   • Authentication
     • username + password to access systems
       • reCaptcha to verify user is not bot
         • online bot submit data automatically

3. MAINTAINABILITY

   • make other programmers understand coding
     • use comments to:
       • section program
         • explain functions
   • indentation for every selection + iteration branch
     • use descriptive variable names
       • use procedures + functions to structure + eliminate duplicated code
         • constants declared at top

4. TESTING

   • Why?
     • ensure no errors in code
       • check if acceptable performance
         • ensure unauthorised access is prevented
           • test against requirements
   • The Types
     • Iterative Testing
       • while software is being developed
         • checked for functionality
           • easy to identify errors in existing code
     • Terminal/Final Testing
       • performed when program is finished
         • test that all modules work together
           • test if it produces required results with:
             • valid, invalid and borderline