rev-list tests: don't hide abort() in "test_expect_failure"

Change a couple of uses of "test_expect_failure" to use a
"test_expect_success" to positively assert the current behavior, and
replace the intent of "test_expect_failure" with a "TODO" comment int
the description.

As noted in [1] the "test_expect_failure" feature is overly eager to
accept any failure as OK, and thus by design hides segfaults, abort()
etc. Because of that I didn't notice in dd9cede (leak tests: mark
some rev-list tests as passing with SANITIZE=leak, 2021-10-31) that
this test leaks memory under SANITIZE=leak.

I have some larger local changes to add a better
"test_expect_failure", which would work just like
"test_expect_success", but would allow us say "test_todo" here (and
"success" would emit a "not ok [...] # TODO", not "ok [...]".

So even though using "test_expect_success" here comes with its own
problems[2], let's use it as a narrow change to fix the problem at
hand here and stop conflating the current "success" with actual
SANITIZE=leak failures.

1. https://lore.kernel.org/git/[email protected]/
2. https://lore.kernel.org/git/[email protected]/

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

t/t6102-rev-list-unexpected-objects.sh

@@ -17,8 +17,13 @@ test_expect_success 'setup unexpected non-blob entry' '
 	broken_tree="$(git hash-object -w --literally -t tree broken-tree)"
 '
 
-test_expect_failure 'traverse unexpected non-blob entry (lone)' '
-	test_must_fail git rev-list --objects $broken_tree
+test_expect_success !SANITIZE_LEAK 'TODO (should fail!): traverse unexpected non-blob entry (lone)' '
+	sed "s/Z$//" >expect <<-EOF &&
+	$broken_tree Z
+	$tree foo
+	EOF
+	git rev-list --objects $broken_tree >actual &&
+	test_cmp expect actual
 '
 
 test_expect_success 'traverse unexpected non-blob entry (seen)' '
@@ -116,8 +121,8 @@ test_expect_success 'setup unexpected non-blob tag' '
 	tag=$(git hash-object -w --literally -t tag broken-tag)
 '
 
-test_expect_failure 'traverse unexpected non-blob tag (lone)' '
-	test_must_fail git rev-list --objects $tag
+test_expect_success !SANITIZE_LEAK 'TODO (should fail!): traverse unexpected non-blob tag (lone)' '
+	git rev-list --objects $tag
 '
 
 test_expect_success 'traverse unexpected non-blob tag (seen)' '