Some observations about testing:

• Testing can uncover examples for which a program fails.
• Most programs accept a sufficiently wide range of inputs that one cannot possibly test all possible inputs.
• Thus, testing cannot prove total correctness.

Examples:

• Space Shuttle Ground Processing System
  • over 500,000 lines of code
  • one of largest real-time systems developed
  • over 2177 hours of testing
  • errors classified as "critical", "major", or "minor"
  • Tally of errors found:

    	Critical	Major	Minor
    Testing	3	76	128
    Mission	1	3	20

  • Conclusion from Limit's Text: "Thus, while many errors were caught during extensive testing and simulation, a fair number of problems were not encountered until the mission itself."

  Original Source: Misra, "Software Reliability Analysis," IBM System Journal, Volume 22, Number 3, 1983, quoted in Software Engineering Notes October 1989. Volume 11, Number 5, page 16.

created: 3 January 2007 last revised: 7 January 2007

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