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TotT: Too Many Tests

Thursday, February 21, 2008
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8 comments :

  1. BenFebruary 21, 2008 at 11:59:00 AM PST

    Great example! A suggestion if I may?

    The 27 test example doesn't take advantage of the independence provided by OR. One doesn't need to test every combination of pairs, as there is no conditional logic between them. Consider:

    A = B, C = D, E = F : DoAnother()
    A < B, C < D, E < F : DoAnother()
    A > B, C < D, E < F : DoOneThing()
    A < B, C > D, E < F : DoOneThing()
    A < B, C < D, E > F : DoOneThing()

    That's five tests, but it tests equivalence, greater than, and less than for each pair.

    This provides the same confidence as the 27 test example, with half the tests of the decreased encapsulation example.

    -Ben

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  2. Rob BaillieFebruary 22, 2008 at 1:20:00 AM PST

    And if one of the 'OR's changed to an 'XOR', the tests would still pass, but the behaviour would change.

    Taking advantage of the logical independence of OR produces a gap due to its reliance on the use of OR.

    Mind you whilst the level confidence may not be the same as with the 27 test example, the drop may not be particularly significant, thus illustrating the original point I suppose.

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  3. Gary BruntonFebruary 22, 2008 at 8:09:00 AM PST

    You mention, "Limit the exposure by controlling scope appropriately, as we did in the Java code above.".

    I'm not a java guy but it appears to me that you've made the extracted functions private and not testable from outside this class.

    What am I missing?

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  4. TimFebruary 22, 2008 at 8:23:00 AM PST

    Gary, the first comment under the first extracted conditional indicates the visibility which is package.

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  5. Gary BruntonFebruary 22, 2008 at 8:40:00 AM PST

    Thanks Tim.

    Just not paying close enough attention.

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  6. dastelsFebruary 25, 2008 at 2:00:00 PM PST

    yes... the format of this blog isn't as code friendly as an 8.5x11 page. I've been playing with the code format. Small font, or break the lines... sometimes with resulting oddness. Comments on that appreciated.

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  7. AnonymousMarch 3, 2008 at 5:37:00 AM PST

    It is also interesting to look at the NPath complexity metric for a function or method as it gives you a pretty good estimate of how many tests you need.

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  8. nongolosJune 5, 2009 at 5:04:00 AM PDT

    Good example of equivalence class partioning.

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