pack-objects tests: don't leave test .git corrupt at end

Change the pack-objects tests to not leave their .git directory
corrupt and the end.

In 2fca19f ("fix multiple issues with t5300", 2010-02-03) a comment
was added warning against adding any subsequent tests, but since
4614043 ("index-pack: use streaming interface for collision test on
large blobs", 2012-05-24) the comment has drifted away from the code,
mentioning two test, when we actually have three.

Instead of having this warning let's just create a new .git directory
specifically for these tests.

As an aside, it would be interesting to instrument the test suite to
run a "git fsck" at the very end (in "test_done"). That would have
errored before this change, and may find other issues #leftoverbits.

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

Author: avar

t/t5300-pack-object.sh

@@ -468,29 +468,32 @@ test_expect_success 'pack-objects in too-many-packs mode' '
 	git fsck
 '
 
-#
-# WARNING!
-#
-# The following test is destructive.  Please keep the next
-# two tests at the end of this file.
-#
-
-test_expect_success 'fake a SHA1 hash collision' '
-	long_a=$(git hash-object a | sed -e "s!^..!&/!") &&
-	long_b=$(git hash-object b | sed -e "s!^..!&/!") &&
-	test -f	.git/objects/$long_b &&
-	cp -f	.git/objects/$long_a \
-		.git/objects/$long_b
+test_expect_success 'setup: fake a SHA1 hash collision' '
+	git init corrupt &&
+	(
+		cd corrupt &&
+		long_a=$(git hash-object -w ../a | sed -e "s!^..!&/!") &&
+		long_b=$(git hash-object -w ../b | sed -e "s!^..!&/!") &&
+		test -f	.git/objects/$long_b &&
+		cp -f	.git/objects/$long_a \
+			.git/objects/$long_b
+	)
 '
 
 test_expect_success 'make sure index-pack detects the SHA1 collision' '
-	test_must_fail git index-pack -o bad.idx test-3.pack 2>msg &&
-	test_i18ngrep "SHA1 COLLISION FOUND" msg
+	(
+		cd corrupt &&
+		test_must_fail git index-pack -o ../bad.idx ../test-3.pack 2>msg &&
+		test_i18ngrep "SHA1 COLLISION FOUND" msg
+	)
 '
 
 test_expect_success 'make sure index-pack detects the SHA1 collision (large blobs)' '
-	test_must_fail git -c core.bigfilethreshold=1 index-pack -o bad.idx test-3.pack 2>msg &&
-	test_i18ngrep "SHA1 COLLISION FOUND" msg
+	(
+		cd corrupt &&
+		test_must_fail git -c core.bigfilethreshold=1 index-pack -o ../bad.idx ../test-3.pack 2>msg &&
+		test_i18ngrep "SHA1 COLLISION FOUND" msg
+	)
 '
 
 test_done