t9301: make hash size independent

Instead of using a hard-coded all-zeros object ID, use $ZERO_OID.
Compute the length of the object IDs in use and use this instead of
hard-coding the constant 40.

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/t9301-fast-import-notes.sh

@@ -470,12 +470,13 @@ test_expect_success 'add lots of commits and notes' '
 '
 
 test_expect_success 'verify that lots of notes trigger a fanout scheme' '
+	hexsz=$(test_oid hexsz) &&
 
 	# None of the entries in the top-level notes tree should be a full SHA1
 	git ls-tree --name-only refs/notes/many_notes |
 	while read path
 	do
-		if test $(expr length "$path") -ge 40
+		if test $(expr length "$path") -ge $hexsz
 		then
 			return 1
 		fi
@@ -518,7 +519,7 @@ test_expect_success 'verify that importing a notes tree respects the fanout sche
 	git ls-tree --name-only refs/notes/other_notes |
 	while read path
 	do
-		if test $(expr length "$path") -ge 40
+		if test $(expr length "$path") -ge $hexsz
 		then
 			return 1
 		fi
@@ -593,7 +594,7 @@ test_expect_success 'verify that changing notes respect existing fanout' '
 	git ls-tree --name-only refs/notes/many_notes |
 	while read path
 	do
-		if test $(expr length "$path") -ge 40
+		if test $(expr length "$path") -ge $hexsz
 		then
 			return 1
 		fi
@@ -616,7 +617,7 @@ i=$(($num_commits - $remaining_notes))
 for sha1 in $(git rev-list -n $i refs/heads/many_commits)
 do
 	cat >>input <<INPUT_END
-N 0000000000000000000000000000000000000000 $sha1
+N $ZERO_OID $sha1
 INPUT_END
 done
 
@@ -646,7 +647,6 @@ test_expect_success 'remove lots of notes' '
 '
 
 test_expect_success 'verify that removing notes trigger fanout consolidation' '
-
 	# All entries in the top-level notes tree should be a full SHA1
 	git ls-tree --name-only -r refs/notes/many_notes |
 	while read path
@@ -656,7 +656,7 @@ test_expect_success 'verify that removing notes trigger fanout consolidation' '
 		test "$path" = "deadbeef" && continue
 		test "$path" = "de/adbeef" && continue
 
-		if test $(expr length "$path") -ne 40
+		if test $(expr length "$path") -ne $hexsz
 		then
 			return 1
 		fi