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Re: [XP] Test-first an infinite loop

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  • Adam Sroka
    I don t see what s so hard about this. You just need to connect your test harness to your time traveling hot tub, go to the Restaurant at the End of the
    Message 1 of 31 , Apr 4 7:26 PM
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      I don't see what's so hard about this. You just need to connect your
      test harness to your time traveling hot tub, go to the Restaurant at
      the End of the Universe, and make sure that it's still running.
      Simple.

      On Sun, Apr 4, 2010 at 7:22 PM, Ron Jeffries <ronjeffries@...> wrote:
      >
      >
      >
      > Hello, Bill. On Sunday, April 4, 2010, at 5:50:02 PM, you wrote:
      >
      > > This is one of those test-first situations that I'm never happy with:
      > > How to implement a requirement that a process not terminate (or
      > > possibly until some external stimuli like a signal or kill file is
      > > triggered) test-first?
      >
      > This reminds me of the halting problem, and if I were clever I could
      > probably reduce it to that. In some sense, there is no way to prove
      > that a program runs forever by testing it.
      >
      > It may well be easier to prove that it runs forever by analyzing it.
      >
      > For example, a loop inside an exception handler that restarts the
      > loop will visibly run forever ...
      >
      > I suspect, though, that what we are really interested in isn't "runs
      > forever" so much as "handles or avoids everything that could go
      > wrong". Some of that we can test directly, but some issues, such as
      > have been discussed, seem only to yield, reluctantly, to
      > long-running tests.
      >
      > Ron Jeffries
      > www.XProgramming.com
      > www.xprogramming.com/blog
      > The practices are not the knowing: they are a path to the knowing.
      >
      >
    • Bill Michell
      Well, an infinite loop is definitely a special case construct - not something that you want to see in normal usage. Sounds like what we are looking for is a
      Message 31 of 31 , Apr 9 4:46 AM
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        Well, an infinite loop is definitely a special case construct - not something that you want to see in normal usage.

        Sounds like what we are looking for is a good use case - maybe a daemon that keeps running some processing method even when given no time by the current thread.

        So I'd make the processing method simply increment a counter.

        The first test just sets the counter to 0 and spawns a thread that runs our main method. The test then checks that the counter value eventually becomes at least 1 - and hence that our processing method got called. Note that spawning the thread is probably part of the test, not the method under test.

        No loop required - just a call to our processing method.

        The next test spawns the thread again, but this time checks the counter eventually becomes at least, say, 10.

        I'd posit that the simplest way to pass the test is to surround the worker method call with a while(1) construct. If you wanted to go via ten calls to the worker method first, knock yourself out.

        For completeness, I'd probably write a test that checks the counter with a decent time interval between the checks, and show that the counter value was continuing to increment. If you haven't reached while(1) already, then this test will surely get you there...

        Yes, it isn't a fast test, and yes, it involves spawning threads. Not pretty. But I'd argue that you are working with a special use case here - even though on the face of it, the construct is a really simple one. It also gives a nice clean design (separating the "never stop" from the "processing" stuff) that lets you do nice things like checking error conditions and termination conditions if those ever become interesting.

        On 8 Apr 2010, at 23:09, Tom wrote:

        > Eggzackly - hence my hesitation.
        >
        > --- In extremeprogramming@yahoogroups.com, Adam Sroka <adam.sroka@...> wrote:
        > >
        > > On Thu, Apr 8, 2010 at 11:06 AM, Tom <rossentj@...> wrote:
        > > >
        > > >
        > > >
        > > > I hesitate to suggest such ugly complexity - but ... maybe have the test start the target in a separate thread which it can kill when it's satisfied ... in a "finally" clause, of course....
        > > >
        > >
        > > At which point it may no longer be the simplest thing that could
        > > possibly work ;-)
        > >
        > > How would you change the test so that it was?
        > >
        >
        >

        --
        Bill Michell
        billmichell@...






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