On Sat, Sep 7, 2013 at 11:26 PM, Jeff King <p...@peff.net> wrote:
> On Sat, Sep 07, 2013 at 11:13:10PM -0500, Felipe Contreras wrote:
>> > If the reasoning is "cmp(actual, expect) makes more sense to humans"
>> > then I do not think it is universal.
>> No.
>> ---
>> A(ny) sanely defined "compare A with B" function should yield the
>> result of subtracting B from A, i.e. cmp(A,B) should be like (A-B).
>> That is what you feed qsort() and bsearch() (it is not limited to C;
>> you see the same in "sort { $a <=> $b }").  The definition naturally
>> makes "cmp(A,B) < 0" like "A < B" and "cmp(A,B) > 0" like "A > B".
>> ---
> Ah, you mean "if you think that the compare function should behave like
> C *_cmp functions, it should be A-B". Perhaps it is simply that I do not
> think of the function in those terms, but more like "show me the
> differences from B to A".

But that is the problem, you are unable to ignore the implementation.
You don't see test_cmp(), you see 'diff -u'.

>> > Otherwise why would so many
>> > existing test frameworks do it the other way?
>> Which many existing frameworks do it the other way?
> John mentioned JUnit, NUnit, and PHPUnit earlier in the thread. I
> believe that Ruby's Test::Unit::Assertions also has
> assert_equal(expected, actual).

That's because they all do first expect, then actual.

assert_equal( expected, actual, failure_message = nil )
assert_not_equal( expected, actual, failure_message = nil )

That's why.

>> > Or any number of variations. I'm sure you will say "but those seem
>> > awkward and unlike how I think about it". But that was my point; it
>> > seems to be a matter of preference.
>> Really? You think any sane human being would prefer:
>> Computer, given that we expect B, how does A differ?
>> To:
>> Computer, compare A with B
> I already said that is how I think about it. If you want to call me notn
> sane, feel free. But I do not see that this line of discussion is going
> anywhere productive.

Again, that's because you are already thinking on the resulting diff,
based on the 'diff -u' command, but that's not in question here. Even
if test_cmp() didn't return an diff (it just ran cmp), it would be
useful, as ultimately we want to test for failures. Ultimately what we
want is to check that A is equal to B, so it's natural to tell the
computer "compare A with B", and if you don't think so, then yeah, I
think you are insane.

Felipe Contreras
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