Software Testing

1
Software Testing

• Week 10

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Software Testing

• Is it sufficient that a program runs without
  crashing and produces a result?
• What if the result is only correct sometimes?
• What if, sometimes, the system crashes and
  sometimes it doesnt?
• What can you, the developer, do to get it right
  all the time?

3
Software Testing - the reality

• Impossible to test even simple software for all
  possible combinations of input data!
• Important to choose broad spectrum of
  representative test cases that cover as much as
  possible.
• Two main approaches to testing -
• Black Box
• White Box

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Black Box Testing

• Testing from performance viewpoint
• Assumes cannot see code - black box which
• receives input
• produces output
• how it transforms input into output is hidden

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Black Box Testing

• Test software against stated requirements
• Develop test data sets to examine normal and
  unusual instances
• Program should meet
• functional requirements
• performance requirements, eg
• speed
• ease of use

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White Box Testing

• Assumes total access to code!
• Focus of testing is on program logic
• Test each decision program has to make
• Selection decisions
• Iteration decisions
• Design test data to exercise every possible path
  through code

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White Box Testing

• For example a loop is controlled by condition
• loopnum gt 5
• Need three test cases
• loopnum 4
• loopnum 5
• loopnum 6
• Why?
• To test boundary where true/false changes
• Called boundary testing

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Testing

• Usual to use combination of White Black Box
  approaches
• Is testing your own software the best approach?
• More usual to have a separate team testing
  software - impartial!
• Testing is important to achieve reliability
• Reliability - given a set of input data, program
  should always produce same result

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Testing -Example
Input age If age gt17 Then Display message
You are old enough to drive Else Calulate
number of years until driving allowed (17 -
age) Display appropriate message Endif
10
Error trapping

• This weeks page on the web site has an example
  of a program to write data to a sequential file.
• This does not include any error trapping.
• For example if you try to open a file on a floppy
  disk in drive a and there is no disk there, the
  program will crash (Disk not ready) error
  message-see P 405, Schneider).
• You will be able to think of other instances
  where the program could be improved e.g
  error-trapping so you can not save duplicate
  student numbers.