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

[Junio C Hamano <gitster@pobox.com>]

Andrei Rybak <rybak.a.v@gmail.com> writes:

> On 14/08/18 13:47, SZEDER Gábor wrote:
>> ... both
>> invocations produce empty 'pack{a,b}.objects' files, and the
>> subsequent 'test_cmp' happily finds those two empty files identical.
>
> Is test_cmp ever used for empty files? Would it make sense for
> test_cmp to issue warning when an empty file is being compared?

Typically test_cmp is used to compare the actual output from a
dubious command being tested with the expected output from a
procedure that is known not to be broken (e.g. a run of 'echo', or a
'cat' of here-doc), so at least one side would not be empty.

The test done here is an odd case---it compares output from two
equally dubious processes that are being tested and sees if their
results match.

That said, since we have test_must_be_empty, we could forbid feeding
empty files to test_cmp, after telling everybody that a test that
expects an empty output must use test_must_be_empty.  I do not think
it is a terrible idea.