From: Kent Beck <kentbeck@...>
Date: 2001-12-11T16:42:50+09:00
Subject: [ruby-talk:28183] Re: John Roth dolt (  Re: A challenge to proponents of Unit Testing. )


Tom Adams <tadamsmar@aol.com> wrote in message
news:793af3df.0112101027.1061721f@posting.google.com...
> "Kent Beck" <kentbeck@my-deja.com> wrote in message
news:<9v1ss3$adi$1@suaar1aa.prod.compuserve.com>...
>
> > (Ken's proposed 5 test case solution to Myers Triangle problem was here)
>
> 1. What about oddities in the source code? Like:
>
> if (any side ==4) {
>     return 1;
> }
>
> This would cause it to fail for the test case 1,2,4 and your tests
> would miss that.

Don't put oddities like this in your source code. Working strictly test
first, there would have to be a test that was failing before the conditional
above was written.

> You would need white-box testing to catch this, or you would need
> more, perhaps many more, black-box tests to cover all the possible
> internals of the function's code.
>
> 2. There is also the issue of very large integer values.  At least, you
> can call the function with literal integers where it will fail.  Actually,
> it is not possible to code the function to handle integers of unbounded
> size without using some special integer representations.  Anyway, a
> function would pass your tests with undefined behaviour for very large
> integers.  And, code using the function could work on one compiler or
> machine and fail on another, depending on the language, because of issues
> related to integer size.

Use a sensible language where integers act like integers, not like 32-bit
counter with rollover. If you want to write a Java version of the function,
and show what happens with 2^31, feel free to write those test cases.

The earlier note that I ignored ill-formed triangles (5,5,11) is absolutely
correct. I missed those test cases. I'll post the updated code and tests
later.

Kent