t6500: specify test values for SHA-256

In this test, we want to produce several blobs whose first two hex
characters are "17", since we look at this object directory as a proxy
for how many loose objects there are before we need to GC.  Use
test_oid_cache to specify strings that will hash to the right values
when turned into blobs.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Reviewed-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t6500-gc.sh

@@ -10,7 +10,24 @@ test_expect_success 'setup' '
 	# do not let the amount of physical memory affects gc
 	# behavior, make sure we always pack everything to one pack by
 	# default
-	git config gc.bigPackThreshold 2g
+	git config gc.bigPackThreshold 2g &&
+
+	# These are simply values which, when hashed as a blob with a newline,
+	# produce a hash where the first byte is 0x17 in their respective
+	# algorithms.
+	test_oid_cache <<-EOF
+	obj1 sha1:263
+	obj1 sha256:34
+
+	obj2 sha1:410
+	obj2 sha256:174
+
+	obj3 sha1:523
+	obj3 sha256:313
+
+	obj4 sha1:790
+	obj4 sha256:481
+	EOF
 '
 
 test_expect_success 'gc empty repository' '
@@ -85,13 +102,13 @@ test_expect_success 'auto gc with too many loose objects does not attempt to cre
 	# We need to create two object whose sha1s start with 17
 	# since this is what git gc counts.  As it happens, these
 	# two blobs will do so.
-	test_commit 263 &&
-	test_commit 410 &&
+	test_commit "$(test_oid obj1)" &&
+	test_commit "$(test_oid obj2)" &&
 	# Our first gc will create a pack; our second will create a second pack
 	git gc --auto &&
 	ls .git/objects/pack | sort >existing_packs &&
-	test_commit 523 &&
-	test_commit 790 &&
+	test_commit "$(test_oid obj3)" &&
+	test_commit "$(test_oid obj4)" &&
 
 	git gc --auto 2>err &&
 	test_i18ngrep ! "^warning:" err &&