Re: [PATCH] t5310-pack-bitmaps: fix bogus 'pack-objects to file can use bitmap' test

[Jeff King <peff@peff.net>]

On Sun, Aug 19, 2018 at 11:37:59PM +0200, Andrei Rybak wrote:

> On 19/08/18 22:32, Jeff King wrote:
> > On Sun, Aug 19, 2018 at 07:50:42PM +0200, Andrei Rybak wrote:
> > 
> >>   1. Check both files at the same time (combination with Gábor's
> >>      function):
> >>
> >> 	test_cmp () {
> >> 		if test "$1" != - &&
> >> 		   test "$2" != - &&
> >> 		   ! test -s "$1" && 
> >> 		   ! test -s "$2"
> >> 		then
> >> 			error "bug in test script: using test_cmp to check empty file; use test_must_be_empty instead"
> >> 		fi
> >> 		test_cmp_allow_empty "$@"
> >> 	}
> >>
> >>      This will still be reporting to the developer clearly, but
> >>      will only catch cases exactly like the bogus test in t5310.
> > 
> > Doesn't that have the opposite issue? If we expect non-empty output but
> > the command produces empty output, we'd say "bug in the test script".
> > But that is not true at all; it's a failed test.
> 
> No. Only when both "$1" and "$2" are empty files will the function above
> report "bug in test script". From patch's commit message:

Oh, you're right. Somewhere between the screen and my brain the "&&"
became an "||".

I agree that works, and has the advantage that the arguments are treated
symmetrically. We _might_ say "test failure" instead of "bug in test"
when the expectation is empty and the generated output is not (because
we do not know which is which), but I think that would be uncommon (and
the most important thing is that we do not silently consider it a pass).

> > If we assume that "expect" is first (which is our convention but not
> > necessarily guaranteed), then I think the best logic is something like:
> > 
> >   if $1 is empty; then
> >     bug in the test script
> >   elif test_cmp_allow_empty "$@"
> >     test failure
> > 
> > We do not need to check $2 at all. An empty one is either irrelevant (if
> > the expectation is empty), or a test failure (because it would not match
> > the non-empty $1).
> 
> ... this is indeed a better solution. I written out the cases for
> updated test_cmp to straighten out my thinking:

I'd be OK pursuing either this line, or what you showed originally.

-Peff