Subject: Re: [PATCH v2 1/2] gc: add tests for --cruft and friends

From: Junio C Hamano <[email-masked]>
Date: Wed, 26 Oct 2022 14:03:14 -0700

Taylor Blau <[email-masked]> writes:

> +prepare_cruft_history () {
> +	test_commit base &&
> +
> +	test_commit --no-tag foo &&
> +	test_commit --no-tag bar &&
> +	git reset HEAD^^
> +}

OK.  Three pearls on a single strand, then the tip-two gets rewound
away.

> +assert_cruft_pack_exists () {
> +	find .git/objects/pack -name "*.mtimes" >mtimes &&
> +	sed -e 's/\.mtimes$/\.pack/g' mtimes >packs &&

Somebody recently made comment that we already depend on the fact
that the default action for "find" is "-print".  I do not see the
need for the 'mtimes' intermediary file.  It does not hurt, but it
is not needed.

> +	test_file_not_empty packs &&
> +	while read pack
> +	do
> +		test_path_is_file "$pack" || return 1
> +	done <packs
> +}

OK.  We enumerate .mtimes files and ensure corresponding .pack
exists for each of them.  That might miss a case where we thought we
created a cruft pack (i.e. .pack exists) but somehow failed to
create the matching .mtimes file by mistake, but it is hard to tell
such a "broken cruft pack" file from a normal pack file, so I think
the above is the best we can do.

> +test_expect_success 'gc --cruft generates a cruft pack' '
> +	test_when_finished "rm -fr crufts" &&
> +	git init crufts &&
> +	(
> +		cd crufts &&
> +
> +		prepare_cruft_history &&
> +		git gc --cruft &&
> +		assert_cruft_pack_exists
> +	)
> +'
> +
> +test_expect_success 'gc.cruftPacks=true generates a cruft pack' '
> +	test_when_finished "rm -fr crufts" &&
> +	git init crufts &&
> +	(
> +		cd crufts &&
> +
> +		prepare_cruft_history &&
> +		git -c gc.cruftPacks=true gc &&
> +		assert_cruft_pack_exists
> +	)
> +'

We could instead do away without when-finished clean-up and use
separate test subdirectory.  Consistently doing so may make CI
forensic easier.  I do not think it is necessary in the test history
used here that is too simple to be realisic.  If something breaks at
CI, it is simple enough to reproduce it manually, so I do not think
it is worth a reroll for that.

>  run_and_wait_for_auto_gc () {
>  	# We read stdout from gc for the side effect of waiting until the
>  	# background gc process exits, closing its fd 9.  Furthermore, the