transfer.fsckObjects tests: untangle confusing setup

The tests for transfer.fsckObjects have grown organically over time to
not make much sense.

Initially when these were added in b10a535 ("test: fetch/receive
with fsckobjects", 2011-09-04) they were only testing the "corrupt or
missing object" case, but later on in 70a4ae7 ("fsck: add a simple
test for receive.fsck.<msg-id>", 2015-06-22) they were expanded to
check for the fsck.<msg-id> feature.

The problem was that we still kept the same corrupt test repo, making
it harder to add new tests that check the entirety of the repository
between operations via "git fsck" to see whether only known issues
that can be ignored with fsck.<msg-id> have occurred.

The tests only did the right thing because such a full "git fsck" was
never done after a certain point, and instead we were only
manipulating specific refs. This makes it harder to add new tests, and
none of the fsck.<msg-id> tests relied on this.

So let's not confuse the two and repair the corrupt repository before
we run the fsck.<msg-id> tests.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5504-fetch-receive-strict.sh

@@ -3,13 +3,16 @@
 test_description='fetch/receive strict mode'
 . ./test-lib.sh
 
-test_expect_success setup '
+test_expect_success 'setup and inject "corrupt or missing" object' '
 	echo hello >greetings &&
 	git add greetings &&
 	git commit -m greetings &&
 
 	S=$(git rev-parse :greetings | sed -e "s|^..|&/|") &&
 	X=$(echo bye | git hash-object -w --stdin | sed -e "s|^..|&/|") &&
+	echo $S >S &&
+	echo $X >X &&
+	cp .git/objects/$S .git/objects/$S.back &&
 	mv -f .git/objects/$X .git/objects/$S &&
 
 	test_must_fail git fsck
@@ -115,6 +118,13 @@ test_expect_success 'push with transfer.fsckobjects' '
 	test_cmp exp act
 '
 
+test_expect_success 'repair the "corrupt or missing" object' '
+	mv -f .git/objects/$(cat S) .git/objects/$(cat X) &&
+	mv .git/objects/$(cat S).back .git/objects/$(cat S) &&
+	rm -rf .git/objects/$(cat X) &&
+	git fsck
+'
+
 cat >bogus-commit <<EOF
 tree $EMPTY_TREE
 author Bugs Bunny 1234567890 +0000