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From Richard Liang <richard.lian...@gmail.com>
Subject Re: Unit testing revisited
Date Sun, 02 Apr 2006 15:38:41 GMT
Mikhail Loenko wrote:
> Sorry for bringing this thread back :)
Congratulations, Mikhail .

This is a great thread, indeed :-)

For the following example, I do recommend not to use BUF_LENGTH in check 
method. Just imagining the situation that you wan to set BUF_LENGTH as 
256, but occasionally set it as 255. The "check" will not find this defect.

IMHO, we shall try to test our code from our customers' perspective. 
That is, we shall write test cases through the APIs which our customers 
possibly use. But as you know, testing is always **risk-based**. If you 
have good reason to write test cases through some internal APIs which 
our customers will never use or cannot use, just do it. :-)
> I've just found an example when access to internals helps avoiding
> test modification.
> I'm developing an implementation using some internal buffer of length like
> static int BUF_LENGTH = 256;
> To reduce JNI overhead it accumulates data and passes it into native
> function when the buffer is full. Buffer length affects performance and might be
> changed later.
> And I have tests that verify how my implementation works when
> input size is close to the buffer size.
> Currently I do something like
> check(BUF_LENGTH - 1);
> check(BUF_LENGTH );
> check(BUF_LENGTH + 1);
> check(BUF_LENGTH *2);
> And the 'check' method tests API only. If later I decide to change
> internal buffer
> size I'll not have to change the test. But if I had hardcoded
> constants in the test
> then I could later change buf size forgetting to change the test and leaving
> boundary conditions untested.
> Thanks,
> Mikhail
> 2006/3/27, Mikhail Loenko <mloenko@gmail.com>:
>> Hi Richard,
>>> Why? IMHO, it's easier to write test cases through public API. And the
>>> internals may possibly change, so if we write test cases directly for
>>> the internals, our test cases will not be stable.
>> One of examples might be: to test something trough public API
>> you need a test of 1000 lines of code, but if you can access internals,
>> 10 lines is enough
>> Thanks,
>> Mikhail

Richard Liang
China Software Development Lab, IBM 

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