Merge branch 'bc/hash-independent-tests'

Many tests hardcode the raw object names, which would change once we migrate away from SHA-1. While some of them must test against exact object names, most of them do not have to use hardcoded constants in the test. The latter kind of tests have been updated to test the moral equivalent of the original without hardcoding the actual object names. * bc/hash-independent-tests: (28 commits) t5300: abstract away SHA-1-specific constants t4208: abstract away SHA-1-specific constants t4045: abstract away SHA-1-specific constants t4042: abstract away SHA-1-specific constants t4205: sort log output in a hash-independent way t/lib-diff-alternative: abstract away SHA-1-specific constants t4030: abstract away SHA-1-specific constants t4029: abstract away SHA-1-specific constants t4029: fix test indentation t4022: abstract away SHA-1-specific constants t4020: abstract away SHA-1-specific constants t4014: abstract away SHA-1-specific constants t4008: abstract away SHA-1-specific constants t4007: abstract away SHA-1-specific constants t3905: abstract away SHA-1-specific constants t3702: abstract away SHA-1-specific constants t3103: abstract away SHA-1-specific constants t2203: abstract away SHA-1-specific constants t: skip pack tests if not using SHA-1 t4044: skip test if not using SHA-1 ...
2018-05-30 21:51:28 +09:00 · 2018-05-30 21:51:28 +09:00 · 9472b13201
--- a/t/diff-lib.sh
+++ b/t/diff-lib.sh
@ -1,6 +1,6 @@
 :

-sanitize_diff_raw='/^:/s/ '"\($_x40\)"' '"\($_x40\)"' \([A-Z]\)[0-9]*	/ \1 \2 \3#	/'
+sanitize_diff_raw='/^:/s/ '"\($OID_REGEX\)"' '"\($OID_REGEX\)"' \([A-Z]\)[0-9]*	/ \1 \2 \3#	/'
 compare_diff_raw () {
    # When heuristics are improved, the score numbers would change.
    # Ignore them while comparing.
@ -12,7 +12,7 @@ compare_diff_raw () {
    test_cmp .tmp-1 .tmp-2 && rm -f .tmp-1 .tmp-2
 }

-sanitize_diff_raw_z='/^:/s/ '"$_x40"' '"$_x40"' \([A-Z]\)[0-9]*$/ X X \1#/'
+sanitize_diff_raw_z='/^:/s/ '"$OID_REGEX"' '"$OID_REGEX"' \([A-Z]\)[0-9]*$/ X X \1#/'
 compare_diff_raw_z () {
    # When heuristics are improved, the score numbers would change.
    # Ignore them while comparing.
--- a/t/lib-diff-alternative.sh
+++ b/t/lib-diff-alternative.sh
@ -59,9 +59,11 @@ int main(int argc, char **argv)
 }
 EOF

-	cat >expect <<\EOF
+	file1=$(git rev-parse --short $(git hash-object file1))
+	file2=$(git rev-parse --short $(git hash-object file2))
+	cat >expect <<EOF
 diff --git a/file1 b/file2
-index 6faa5a3..e3af329 100644
+index $file1..$file2 100644
 --- a/file1
 +++ b/file2
@@ -1,26 +1,25 @@
@ -136,9 +138,11 @@ e
 f
 EOF

-	cat >expect <<\EOF
+	uniq1=$(git rev-parse --short $(git hash-object uniq1))
+	uniq2=$(git rev-parse --short $(git hash-object uniq2))
+	cat >expect <<EOF
 diff --git a/uniq1 b/uniq2
-index b414108..0fdf397 100644
+index $uniq1..$uniq2 100644
 --- a/uniq1
 +++ b/uniq2
@@ -1,6 +1,6 @@
--- a/t/t0000-basic.sh
+++ b/t/t0000-basic.sh
@ -839,7 +839,7 @@ test_expect_success 'writing tree out with git write-tree' '
 '

 # we know the shape and contents of the tree and know the object ID for it.
-test_expect_success 'validate object ID of a known tree' '
+test_expect_success SHA1 'validate object ID of a known tree' '
 	test "$tree" = 7bb943559a305bdd6bdee2cef6e5df2413c3d30a
    '

@ -882,7 +882,7 @@ test_expect_success 'showing stage with git ls-files --stage' '
 	git ls-files --stage >current
 '

-test_expect_success 'validate git ls-files output for a known tree' '
+test_expect_success SHA1 'validate git ls-files output for a known tree' '
 	cat >expected <<-\EOF &&
 	100644 f87290f8eb2cbbea7857214459a0739927eab154 0	path0
 	120000 15a98433ae33114b085f3eb3bb03b832b3180a01 0	path0sym
@ -900,7 +900,7 @@ test_expect_success 'writing tree out with git write-tree' '
 	tree=$(git write-tree)
 '

-test_expect_success 'validate object ID for a known tree' '
+test_expect_success SHA1 'validate object ID for a known tree' '
 	test "$tree" = 087704a96baf1c2d1c869a8b084481e121c88b5b
 '

@ -908,7 +908,7 @@ test_expect_success 'showing tree with git ls-tree' '
    git ls-tree $tree >current
 '

-test_expect_success 'git ls-tree output for a known tree' '
+test_expect_success SHA1 'git ls-tree output for a known tree' '
 	cat >expected <<-\EOF &&
 	100644 blob f87290f8eb2cbbea7857214459a0739927eab154	path0
 	120000 blob 15a98433ae33114b085f3eb3bb03b832b3180a01	path0sym
@ -924,7 +924,7 @@ test_expect_success 'showing tree with git ls-tree -r' '
 	git ls-tree -r $tree >current
 '

-test_expect_success 'git ls-tree -r output for a known tree' '
+test_expect_success SHA1 'git ls-tree -r output for a known tree' '
 	cat >expected <<-\EOF &&
 	100644 blob f87290f8eb2cbbea7857214459a0739927eab154	path0
 	120000 blob 15a98433ae33114b085f3eb3bb03b832b3180a01	path0sym
@ -943,7 +943,7 @@ test_expect_success 'showing tree with git ls-tree -r -t' '
 	git ls-tree -r -t $tree >current
 '

-test_expect_success 'git ls-tree -r output for a known tree' '
+test_expect_success SHA1 'git ls-tree -r output for a known tree' '
 	cat >expected <<-\EOF &&
 	100644 blob f87290f8eb2cbbea7857214459a0739927eab154	path0
 	120000 blob 15a98433ae33114b085f3eb3bb03b832b3180a01	path0sym
@ -964,7 +964,7 @@ test_expect_success 'writing partial tree out with git write-tree --prefix' '
 	ptree=$(git write-tree --prefix=path3)
 '

-test_expect_success 'validate object ID for a known tree' '
+test_expect_success SHA1 'validate object ID for a known tree' '
 	test "$ptree" = 21ae8269cacbe57ae09138dcc3a2887f904d02b3
 '

@ -972,7 +972,7 @@ test_expect_success 'writing partial tree out with git write-tree --prefix' '
 	ptree=$(git write-tree --prefix=path3/subp3)
 '

-test_expect_success 'validate object ID for a known tree' '
+test_expect_success SHA1 'validate object ID for a known tree' '
 	test "$ptree" = 3c5e5399f3a333eddecce7a9b9465b63f65f51e2
 '

@ -1006,7 +1006,7 @@ test_expect_success 'git read-tree followed by write-tree should be idempotent'
 	test "$newtree" = "$tree"
 '

-test_expect_success 'validate git diff-files output for a know cache/work tree state' '
+test_expect_success SHA1 'validate git diff-files output for a know cache/work tree state' '
 	cat >expected <<\EOF &&
 :100644 100644 f87290f8eb2cbbea7857214459a0739927eab154 0000000000000000000000000000000000000000 M	path0
 :120000 120000 15a98433ae33114b085f3eb3bb03b832b3180a01 0000000000000000000000000000000000000000 M	path0sym
@ -1033,21 +1033,21 @@ test_expect_success 'no diff after checkout and git update-index --refresh' '
 ################################################################
 P=087704a96baf1c2d1c869a8b084481e121c88b5b

-test_expect_success 'git commit-tree records the correct tree in a commit' '
+test_expect_success SHA1 'git commit-tree records the correct tree in a commit' '
 	commit0=$(echo NO | git commit-tree $P) &&
 	tree=$(git show --pretty=raw $commit0 |
 		 sed -n -e "s/^tree //p" -e "/^author /q") &&
 	test "z$tree" = "z$P"
 '

-test_expect_success 'git commit-tree records the correct parent in a commit' '
+test_expect_success SHA1 'git commit-tree records the correct parent in a commit' '
 	commit1=$(echo NO | git commit-tree $P -p $commit0) &&
 	parent=$(git show --pretty=raw $commit1 |
 		sed -n -e "s/^parent //p" -e "/^author /q") &&
 	test "z$commit0" = "z$parent"
 '

-test_expect_success 'git commit-tree omits duplicated parent in a commit' '
+test_expect_success SHA1 'git commit-tree omits duplicated parent in a commit' '
 	commit2=$(echo NO | git commit-tree $P -p $commit0 -p $commit0) &&
 	     parent=$(git show --pretty=raw $commit2 |
 		sed -n -e "s/^parent //p" -e "/^author /q" |
--- a/t/t0090-cache-tree.sh
+++ b/t/t0090-cache-tree.sh
@ -9,7 +9,7 @@ cache-tree extension.

 cmp_cache_tree () {
 	test-tool dump-cache-tree | sed -e '/#(ref)/d' >actual &&
-	sed "s/$_x40/SHA/" <actual >filtered &&
+	sed "s/$OID_REGEX/SHA/" <actual >filtered &&
 	test_cmp "$1" filtered
 }

--- a/t/t1000-read-tree-m-3way.sh
+++ b/t/t1000-read-tree-m-3way.sh
@ -128,7 +128,7 @@ cat >expected <<\EOF
 EOF

 check_result () {
-	git ls-files --stage | sed -e 's/ '"$_x40"' / X /' >current &&
+	git ls-files --stage | sed -e 's/ '"$OID_REGEX"' / X /' >current &&
 	test_cmp expected current
 }

--- a/t/t1001-read-tree-m-2way.sh
+++ b/t/t1001-read-tree-m-2way.sh
@ -30,7 +30,7 @@ read_tree_twoway () {
 compare_change () {
 	sed -n >current \
 	    -e '/^--- /d; /^+++ /d; /^@@ /d;' \
-	    -e 's/^\([-+][0-7][0-7][0-7][0-7][0-7][0-7]\) '"$_x40"' /\1 X /p' \
+	    -e 's/^\([-+][0-7][0-7][0-7][0-7][0-7][0-7]\) '"$OID_REGEX"' /\1 X /p' \
 	    "$1"
 	test_cmp expected current
 }
--- a/t/t1002-read-tree-m-u-2way.sh
+++ b/t/t1002-read-tree-m-u-2way.sh
@ -16,7 +16,7 @@ compare_change () {
 	    -e '1{/^diff --git /d;}' \
 	    -e '2{/^index /d;}' \
 	    -e '/^--- /d; /^+++ /d; /^@@ /d;' \
-	    -e 's/^\(.[0-7][0-7][0-7][0-7][0-7][0-7]\) '"$_x40"' /\1 X /' "$1"
+	    -e 's/^\(.[0-7][0-7][0-7][0-7][0-7][0-7]\) '"$OID_REGEX"' /\1 X /' "$1"
 	test_cmp expected current
 }

--- a/t/t1006-cat-file.sh
+++ b/t/t1006-cat-file.sh
@ -236,8 +236,8 @@ test_expect_success "--batch-check for an empty line" '
 '

 test_expect_success 'empty --batch-check notices missing object' '
-	echo "$_z40 missing" >expect &&
-	echo "$_z40" | git cat-file --batch-check="" >actual &&
+	echo "$ZERO_OID missing" >expect &&
+	echo "$ZERO_OID" | git cat-file --batch-check="" >actual &&
 	test_cmp expect actual
 '

@ -294,8 +294,8 @@ test_expect_success 'setup blobs which are likely to delta' '

 test_expect_success 'confirm that neither loose blob is a delta' '
 	cat >expect <<-EOF &&
-	$_z40
-	$_z40
+	$ZERO_OID
+	$ZERO_OID
 	EOF
 	git cat-file --batch-check="%(deltabase)" <blobs >actual &&
 	test_cmp expect actual
--- a/t/t1007-hash-object.sh
+++ b/t/t1007-hash-object.sh
@ -9,13 +9,13 @@ echo_without_newline() {
 }

 test_blob_does_not_exist() {
-	test_expect_success 'blob does not exist in database' "
+	test_expect_success SHA1 'blob does not exist in database' "
 		test_must_fail git cat-file blob $1
 	"
 }

 test_blob_exists() {
-	test_expect_success 'blob exists in database' "
+	test_expect_success SHA1 'blob exists in database' "
 		git cat-file blob $1
 	"
 }
@ -73,19 +73,19 @@ test_expect_success "Can't use --path with --no-filters" '

 push_repo

-test_expect_success 'hash a file' '
+test_expect_success SHA1 'hash a file' '
 	test $hello_sha1 = $(git hash-object hello)
 '

 test_blob_does_not_exist $hello_sha1

-test_expect_success 'hash from stdin' '
+test_expect_success SHA1 'hash from stdin' '
 	test $example_sha1 = $(git hash-object --stdin < example)
 '

 test_blob_does_not_exist $example_sha1

-test_expect_success 'hash a file and write to database' '
+test_expect_success SHA1 'hash a file and write to database' '
 	test $hello_sha1 = $(git hash-object -w hello)
 '

@ -161,7 +161,7 @@ pop_repo
 for args in "-w --stdin" "--stdin -w"; do
 	push_repo

-	test_expect_success "hash from stdin and write to database ($args)" '
+	test_expect_success SHA1 "hash from stdin and write to database ($args)" '
 		test $example_sha1 = $(git hash-object $args < example)
 	'

@ -176,14 +176,14 @@ example"
 sha1s="$hello_sha1
 $example_sha1"

-test_expect_success "hash two files with names on stdin" '
+test_expect_success SHA1 "hash two files with names on stdin" '
 	test "$sha1s" = "$(echo_without_newline "$filenames" | git hash-object --stdin-paths)"
 '

 for args in "-w --stdin-paths" "--stdin-paths -w"; do
 	push_repo

-	test_expect_success "hash two files with names on stdin and write to database ($args)" '
+	test_expect_success SHA1 "hash two files with names on stdin and write to database ($args)" '
 		test "$sha1s" = "$(echo_without_newline "$filenames" | git hash-object $args)"
 	'

--- a/t/t1012-read-tree-df.sh
+++ b/t/t1012-read-tree-df.sh
@ -32,7 +32,7 @@ settree () {

 checkindex () {
 	git ls-files -s |
-	sed "s|^[0-7][0-7]* $_x40 \([0-3]\)	|\1 |" >current &&
+	sed "s|^[0-7][0-7]* $OID_REGEX \([0-3]\)	|\1 |" >current &&
 	cat >expect &&
 	test_cmp expect current
 }
--- a/t/t1400-update-ref.sh
+++ b/t/t1400-update-ref.sh
@ -6,7 +6,7 @@
 test_description='Test git update-ref and basic ref logging'
 . ./test-lib.sh

-Z=$_z40
+Z=$ZERO_OID

 m=refs/heads/master
 n_dir=refs/heads/gu
--- a/t/t1407-worktree-ref-store.sh
+++ b/t/t1407-worktree-ref-store.sh
@ -50,13 +50,13 @@ test_expect_success 'create_symref(FOO, refs/heads/master)' '
 '

 test_expect_success 'for_each_reflog()' '
-	echo $_z40 > .git/logs/PSEUDO-MAIN &&
+	echo $ZERO_OID > .git/logs/PSEUDO-MAIN &&
 	mkdir -p     .git/logs/refs/bisect &&
-	echo $_z40 > .git/logs/refs/bisect/random &&
+	echo $ZERO_OID > .git/logs/refs/bisect/random &&

-	echo $_z40 > .git/worktrees/wt/logs/PSEUDO-WT &&
+	echo $ZERO_OID > .git/worktrees/wt/logs/PSEUDO-WT &&
 	mkdir -p     .git/worktrees/wt/logs/refs/bisect &&
-	echo $_z40 > .git/worktrees/wt/logs/refs/bisect/wt-random &&
+	echo $ZERO_OID > .git/worktrees/wt/logs/refs/bisect/wt-random &&

 	$RWT for-each-reflog | cut -c 42- | sort >actual &&
 	cat >expected <<-\EOF &&
--- a/t/t1450-fsck.sh
+++ b/t/t1450-fsck.sh
@ -713,7 +713,7 @@ test_expect_success 'fsck notices dangling objects' '

 test_expect_success 'fsck $name notices bogus $name' '
 	test_must_fail git fsck bogus &&
-	test_must_fail git fsck $_z40
+	test_must_fail git fsck $ZERO_OID
 '

 test_expect_success 'bogus head does not fallback to all heads' '
@ -723,7 +723,7 @@ test_expect_success 'bogus head does not fallback to all heads' '
 	blob=$(git rev-parse :foo) &&
 	test_when_finished "git rm --cached foo" &&
 	remove_object $blob &&
-	test_must_fail git fsck $_z40 >out 2>&1 &&
+	test_must_fail git fsck $ZERO_OID >out 2>&1 &&
 	! grep $blob out
 '

--- a/t/t1501-work-tree.sh
+++ b/t/t1501-work-tree.sh
@ -238,10 +238,10 @@ test_expect_success '_gently() groks relative GIT_DIR & GIT_WORK_TREE' '

 test_expect_success 'diff-index respects work tree under .git dir' '
 	cat >diff-index-cached.expected <<-EOF &&
-	:000000 100644 $_z40 $EMPTY_BLOB A	sub/dir/tracked
+	:000000 100644 $ZERO_OID $EMPTY_BLOB A	sub/dir/tracked
 	EOF
 	cat >diff-index.expected <<-EOF &&
-	:000000 100644 $_z40 $_z40 A	sub/dir/tracked
+	:000000 100644 $ZERO_OID $ZERO_OID A	sub/dir/tracked
 	EOF

 	(
@ -257,7 +257,7 @@ test_expect_success 'diff-index respects work tree under .git dir' '

 test_expect_success 'diff-files respects work tree under .git dir' '
 	cat >diff-files.expected <<-EOF &&
-	:100644 100644 $EMPTY_BLOB $_z40 M	sub/dir/tracked
+	:100644 100644 $EMPTY_BLOB $ZERO_OID M	sub/dir/tracked
 	EOF

 	(
--- a/t/t1512-rev-parse-disambiguation.sh
+++ b/t/t1512-rev-parse-disambiguation.sh
@ -22,6 +22,12 @@ one tagged as v1.0.0.  They all have one regular file each.

 . ./test-lib.sh

+if ! test_have_prereq SHA1
+then
+	skip_all='not using SHA-1 for objects'
+	test_done
+fi
+
 test_expect_success 'blob and tree' '
 	test_tick &&
 	(
--- a/t/t1601-index-bogus.sh
+++ b/t/t1601-index-bogus.sh
@ -4,7 +4,7 @@ test_description='test handling of bogus index entries'
 . ./test-lib.sh

 test_expect_success 'create tree with null sha1' '
-	tree=$(printf "160000 commit $_z40\\tbroken\\n" | git mktree)
+	tree=$(printf "160000 commit $ZERO_OID\\tbroken\\n" | git mktree)
 '

 test_expect_success 'read-tree refuses to read null sha1' '
--- a/t/t1700-split-index.sh
+++ b/t/t1700-split-index.sh
@ -426,7 +426,7 @@ test_expect_success 'writing split index with null sha1 does not write cache tre
 	git commit -m "commit" &&
 	{
 		git ls-tree HEAD &&
-		printf "160000 commit $_z40\\tbroken\\n"
+		printf "160000 commit $ZERO_OID\\tbroken\\n"
 	} >broken-tree &&
 	echo "add broken entry" >msg &&

--- a/t/t2011-checkout-invalid-head.sh
+++ b/t/t2011-checkout-invalid-head.sh
@ -15,7 +15,7 @@ test_expect_success 'checkout should not start branch from a tree' '
 '

 test_expect_success 'checkout master from invalid HEAD' '
-	echo $_z40 >.git/HEAD &&
+	echo $ZERO_OID >.git/HEAD &&
 	git checkout master --
 '

--- a/t/t2025-worktree-add.sh
+++ b/t/t2025-worktree-add.sh
@ -477,7 +477,7 @@ post_checkout_hook () {
 test_expect_success '"add" invokes post-checkout hook (branch)' '
 	post_checkout_hook &&
 	{
-		echo $_z40 $(git rev-parse HEAD) 1 &&
+		echo $ZERO_OID $(git rev-parse HEAD) 1 &&
 		echo $(pwd)/.git/worktrees/gumby &&
 		echo $(pwd)/gumby
 	} >hook.expect &&
@ -488,7 +488,7 @@ test_expect_success '"add" invokes post-checkout hook (branch)' '
 test_expect_success '"add" invokes post-checkout hook (detached)' '
 	post_checkout_hook &&
 	{
-		echo $_z40 $(git rev-parse HEAD) 1 &&
+		echo $ZERO_OID $(git rev-parse HEAD) 1 &&
 		echo $(pwd)/.git/worktrees/grumpy &&
 		echo $(pwd)/grumpy
 	} >hook.expect &&
@ -506,7 +506,7 @@ test_expect_success '"add --no-checkout" suppresses post-checkout hook' '
 test_expect_success '"add" in other worktree invokes post-checkout hook' '
 	post_checkout_hook &&
 	{
-		echo $_z40 $(git rev-parse HEAD) 1 &&
+		echo $ZERO_OID $(git rev-parse HEAD) 1 &&
 		echo $(pwd)/.git/worktrees/guppy &&
 		echo $(pwd)/guppy
 	} >hook.expect &&
@ -518,7 +518,7 @@ test_expect_success '"add" in bare repo invokes post-checkout hook' '
 	rm -rf bare &&
 	git clone --bare . bare &&
 	{
-		echo $_z40 $(git --git-dir=bare rev-parse HEAD) 1 &&
+		echo $ZERO_OID $(git --git-dir=bare rev-parse HEAD) 1 &&
 		echo $(pwd)/bare/worktrees/goozy &&
 		echo $(pwd)/goozy
 	} >hook.expect &&
--- a/t/t2027-worktree-list.sh
+++ b/t/t2027-worktree-list.sh
@ -116,7 +116,7 @@ test_expect_success 'broken main worktree still at the top' '
 		git worktree add linked &&
 		cat >expected <<-EOF &&
 		worktree $(pwd)
-		HEAD $_z40
+		HEAD $ZERO_OID

 		EOF
 		cd linked &&
--- a/t/t2107-update-index-basic.sh
+++ b/t/t2107-update-index-basic.sh
@ -37,7 +37,7 @@ test_expect_success '--cacheinfo does not accept blob null sha1' '
 	echo content >file &&
 	git add file &&
 	git rev-parse :file >expect &&
-	test_must_fail git update-index --cacheinfo 100644 $_z40 file &&
+	test_must_fail git update-index --cacheinfo 100644 $ZERO_OID file &&
 	git rev-parse :file >actual &&
 	test_cmp expect actual
 '
@ -47,7 +47,7 @@ test_expect_success '--cacheinfo does not accept gitlink null sha1' '
 	(cd submodule && test_commit foo) &&
 	git add submodule &&
 	git rev-parse :submodule >expect &&
-	test_must_fail git update-index --cacheinfo 160000 $_z40 submodule &&
+	test_must_fail git update-index --cacheinfo 160000 $ZERO_OID submodule &&
 	git rev-parse :submodule >actual &&
 	test_cmp expect actual
 '
--- a/t/t2201-add-update-typechange.sh
+++ b/t/t2201-add-update-typechange.sh
@ -75,35 +75,35 @@ test_expect_success modify '
 		git ls-tree -r HEAD |
 		sed -e "s/^/:/" -e "
 			/	caskly/{
-				s/	caskly/ $_z40 D&/
+				s/	caskly/ $ZERO_OID D&/
 				s/blob/000000/
 			}
 			/	nitfol/{
-				s/	nitfol/ $_z40 $T_letter&/
+				s/	nitfol/ $ZERO_OID $T_letter&/
 				s/blob/100644/
 			}
 			/	rezrov.bozbar/{
-				s/	rezrov.bozbar/ $_z40 D&/
+				s/	rezrov.bozbar/ $ZERO_OID D&/
 				s/blob/000000/
 			}
 			/	xyzzy/{
-				s/	xyzzy/ $_z40 D&/
+				s/	xyzzy/ $ZERO_OID D&/
 				s/blob/000000/
 			}
 			/	yomin/{
-			    s/	yomin/ $_z40 T&/
+			    s/	yomin/ $ZERO_OID T&/
 				s/blob/160000/
 			}
 		"
 	} >expect &&
 	{
 		cat expect
-		echo ":100644 160000 $_empty $_z40 T	yonk"
-		echo ":100644 000000 $_empty $_z40 D	zifmia"
+		echo ":100644 160000 $_empty $ZERO_OID T	yonk"
+		echo ":100644 000000 $_empty $ZERO_OID D	zifmia"
 	} >expect-files &&
 	{
 		cat expect
-		echo ":000000 160000 $_z40 $_z40 A	yonk"
+		echo ":000000 160000 $ZERO_OID $ZERO_OID A	yonk"
 	} >expect-index &&
 	{
 		echo "100644 $_empty 0	nitfol"
--- a/t/t2203-add-intent.sh
+++ b/t/t2203-add-intent.sh
@ -27,12 +27,12 @@ test_expect_success 'git status' '

 test_expect_success 'git status with porcelain v2' '
 	git status --porcelain=v2 | grep -v "^?" >actual &&
-	nam1=d00491fd7e5bb6fa28c517a0bb32b8b506539d4d &&
-	nam2=ce013625030ba8dba906f756967f9e9ca394464a &&
+	nam1=$(echo 1 | git hash-object --stdin) &&
+	nam2=$(git hash-object elif) &&
 	cat >expect <<-EOF &&
-	1 DA N... 100644 000000 100644 $nam1 $_z40 1.t
-	1 A. N... 000000 100644 100644 $_z40 $nam2 elif
-	1 .A N... 000000 000000 100644 $_z40 $_z40 file
+	1 DA N... 100644 000000 100644 $nam1 $ZERO_OID 1.t
+	1 A. N... 000000 100644 100644 $ZERO_OID $nam2 elif
+	1 .A N... 000000 000000 100644 $ZERO_OID $ZERO_OID file
 	EOF
 	test_cmp expect actual
 '
@ -181,7 +181,7 @@ test_expect_success 'rename detection finds the right names' '
 		EOF
 		test_cmp expected.2 actual.2 &&

-		hash=12f00e90b6ef79117ce6e650416b8cf517099b78 &&
+		hash=$(git hash-object third) &&
 		git status --porcelain=v2 | grep -v "^?" >actual.3 &&
 		cat >expected.3 <<-EOF &&
 		2 .R N... 100644 100644 100644 $hash $hash R100 third	first
@ -212,7 +212,7 @@ test_expect_success 'double rename detection in status' '
 		EOF
 		test_cmp expected.2 actual.2 &&

-		hash=12f00e90b6ef79117ce6e650416b8cf517099b78 &&
+		hash=$(git hash-object third) &&
 		git status --porcelain=v2 | grep -v "^?" >actual.3 &&
 		cat >expected.3 <<-EOF &&
 		2 R. N... 100644 100644 100644 $hash $hash R100 second	first
--- a/t/t3100-ls-tree-restrict.sh
+++ b/t/t3100-ls-tree-restrict.sh
@ -32,7 +32,7 @@ test_expect_success \
     echo $tree'

 test_output () {
-    sed -e "s/ $_x40	/ X	/" <current >check
+    sed -e "s/ $OID_REGEX	/ X	/" <current >check
    test_cmp expected check
 }

--- a/t/t3101-ls-tree-dirname.sh
+++ b/t/t3101-ls-tree-dirname.sh
@ -40,7 +40,7 @@ test_expect_success 'setup' '
 '

 test_output () {
-	sed -e "s/ $_x40	/ X	/" <current >check &&
+	sed -e "s/ $OID_REGEX	/ X	/" <current >check &&
 	test_cmp expected check
 }

--- a/t/t3103-ls-tree-misc.sh
+++ b/t/t3103-ls-tree-misc.sh
@ -17,7 +17,8 @@ test_expect_success 'setup' '
 '

 test_expect_success 'ls-tree fails with non-zero exit code on broken tree' '
-	rm -f .git/objects/5f/cffbd6e4c5c5b8d81f5e9314b20e338e3ffff5 &&
+	tree=$(git rev-parse HEAD:a) &&
+	rm -f .git/objects/$(echo $tree | sed -e "s,^\(..\),\1/,") &&
 	test_must_fail git ls-tree -r HEAD
 '

--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@ -47,7 +47,7 @@ test_expect_success 'git branch HEAD should fail' '
 '

 cat >expect <<EOF
-$_z40 $HEAD $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> 1117150200 +0000	branch: Created from master
+$ZERO_OID $HEAD $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> 1117150200 +0000	branch: Created from master
 EOF
 test_expect_success 'git branch -l d/e/f should create a branch and a log' '
 	GIT_COMMITTER_DATE="2005-05-26 23:30" \
@ -901,7 +901,7 @@ test_expect_success '--set-upstream-to notices an error to set branch as own ups

 # Keep this test last, as it changes the current branch
 cat >expect <<EOF
-$_z40 $HEAD $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> 1117150200 +0000	branch: Created from master
+$ZERO_OID $HEAD $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> 1117150200 +0000	branch: Created from master
 EOF
 test_expect_success 'git checkout -b g/h/i -l should create a branch and a log' '
 	GIT_COMMITTER_DATE="2005-05-26 23:30" \
--- a/t/t3510-cherry-pick-sequence.sh
+++ b/t/t3510-cherry-pick-sequence.sh
@ -122,7 +122,7 @@ test_expect_success '--quit keeps HEAD and conflicted index intact' '
 	{
 		git rev-list HEAD |
 		git diff-tree --root --stdin |
-		sed "s/$_x40/OBJID/g"
+		sed "s/$OID_REGEX/OBJID/g"
 	} >actual &&
 	test_cmp expect actual
 '
@ -220,7 +220,7 @@ test_expect_success 'cherry-pick still writes sequencer state when one commit is
 	{
 		git rev-list HEAD |
 		git diff-tree --root --stdin |
-		sed "s/$_x40/OBJID/g"
+		sed "s/$OID_REGEX/OBJID/g"
 	} >actual &&
 	cat >expect <<-\EOF &&
 	OBJID
@ -317,7 +317,7 @@ test_expect_success '--continue after resolving conflicts' '
 	{
 		git rev-list HEAD |
 		git diff-tree --root --stdin |
-		sed "s/$_x40/OBJID/g"
+		sed "s/$OID_REGEX/OBJID/g"
 	} >actual.log &&
 	test_cmp expect foo &&
 	test_cmp expect.log actual.log
@ -334,7 +334,7 @@ test_expect_success '--continue after resolving conflicts and committing' '
 	{
 		git rev-list HEAD |
 		git diff-tree --root --stdin |
-		sed "s/$_x40/OBJID/g"
+		sed "s/$OID_REGEX/OBJID/g"
 	} >actual &&
 	cat >expect <<-\EOF &&
 	OBJID
--- a/t/t3702-add-edit.sh
+++ b/t/t3702-add-edit.sh
@ -40,7 +40,6 @@ test_expect_success 'setup' '

 cat > expected-patch << EOF
 diff --git a/file b/file
-index b9834b5..9020acb 100644
 --- a/file
 +++ b/file
@@ -1,11 +1,6 @@
@ -80,7 +79,6 @@ EOF

 cat > expected << EOF
 diff --git a/file b/file
-index b9834b5..ef6e94c 100644
 --- a/file
 +++ b/file
@@ -1,10 +1,12 @@
@ -100,7 +98,7 @@ EOF

 echo "#!$SHELL_PATH" >fake-editor.sh
 cat >> fake-editor.sh <<\EOF
-mv -f "$1" orig-patch &&
+egrep -v '^index' "$1" >orig-patch &&
 mv -f patch "$1"
 EOF

@ -113,7 +111,8 @@ test_expect_success 'add -e' '
 	git add -e &&
 	test_cmp second-part file &&
 	test_cmp orig-patch expected-patch &&
-	git diff --cached > out &&
+	git diff --cached >actual &&
+	grep -v index actual >out &&
 	test_cmp out expected

 '
--- a/t/t3905-stash-include-untracked.sh
+++ b/t/t3905-stash-include-untracked.sh
@ -35,24 +35,26 @@ test_expect_success 'stash save --include-untracked cleaned the untracked files'
 	test_cmp expect actual
 '

+tracked=$(git rev-parse --short $(echo 1 | git hash-object --stdin))
+untracked=$(git rev-parse --short $(echo untracked | git hash-object --stdin))
 cat > expect.diff <<EOF
 diff --git a/HEAD b/HEAD
 new file mode 100644
-index 0000000..d00491f
+index 0000000..$tracked
 --- /dev/null
 +++ b/HEAD
@@ -0,0 +1 @@
 +1
 diff --git a/file2 b/file2
 new file mode 100644
-index 0000000..d00491f
+index 0000000..$tracked
 --- /dev/null
 +++ b/file2
@@ -0,0 +1 @@
 +1
 diff --git a/untracked/untracked b/untracked/untracked
 new file mode 100644
-index 0000000..5a72eb2
+index 0000000..$untracked
 --- /dev/null
 +++ b/untracked/untracked
@@ -0,0 +1 @@
@ -109,10 +111,11 @@ test_expect_success 'stash save -u dirty index' '
 	git stash -u
 '

+blob=$(git rev-parse --short $(echo 4 | git hash-object --stdin))
 cat > expect <<EOF
 diff --git a/file3 b/file3
 new file mode 100644
-index 0000000..b8626c4
+index 0000000..$blob
 --- /dev/null
 +++ b/file3
@@ -0,0 +1 @@
--- a/t/t4002-diff-basic.sh
+++ b/t/t4002-diff-basic.sh
@ -131,7 +131,7 @@ cmp_diff_files_output () {
    # object ID for the changed files because it wants you to look at the
    # filesystem.
    sed <"$2" >.test-tmp \
-	-e '/^:000000 /d;s/'$_x40'\( [MCRNDU][0-9]*\)	/'$_z40'\1	/' &&
+	-e '/^:000000 /d;s/'$OID_REGEX'\( [MCRNDU][0-9]*\)	/'$ZERO_OID'\1	/' &&
    test_cmp "$1" .test-tmp
 }

--- a/t/t4006-diff-mode.sh
+++ b/t/t4006-diff-mode.sh
@ -8,7 +8,7 @@ test_description='Test mode change diffs.
 '
 . ./test-lib.sh

-sed_script='s/\(:100644 100755\) \('"$_x40"'\) \2 /\1 X X /'
+sed_script='s/\(:100644 100755\) \('"$OID_REGEX"'\) \2 /\1 X X /'

 test_expect_success 'setup' '
 	echo frotz >rezrov &&
--- a/t/t4007-rename-3.sh
+++ b/t/t4007-rename-3.sh
@ -17,6 +17,7 @@ test_expect_success 'prepare reference tree' '
 	echo $tree
 '

+blob=$(git hash-object "$TEST_DIRECTORY/diff-lib/COPYING")
 test_expect_success 'prepare work tree' '
 	cp path0/COPYING path1/COPYING &&
 	git update-index --add --remove path0/COPYING path1/COPYING
@ -26,8 +27,8 @@ test_expect_success 'prepare work tree' '
 # path1 both have COPYING and the latter is a copy of path0/COPYING.
 # Comparing the full tree with cache should tell us so.

-cat >expected <<\EOF
-:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 6ff87c4664981e4397625791c8ea3bbb5f2279a3 C100	path0/COPYING	path1/COPYING
+cat >expected <<EOF
+:100644 100644 $blob $blob C100	path0/COPYING	path1/COPYING
 EOF

 test_expect_success 'copy detection' '
@ -46,8 +47,8 @@ test_expect_success 'copy detection, cached' '
 # path1/COPYING suddenly appearing from nowhere, not detected as
 # a copy from path0/COPYING.

-cat >expected <<\EOF
-:000000 100644 0000000000000000000000000000000000000000 6ff87c4664981e4397625791c8ea3bbb5f2279a3 A	path1/COPYING
+cat >expected <<EOF
+:000000 100644 $ZERO_OID $blob A	path1/COPYING
 EOF

 test_expect_success 'copy, limited to a subtree' '
@ -64,8 +65,8 @@ test_expect_success 'tweak work tree' '
 # path0/COPYING.  Showing the full tree with cache should tell us about
 # the rename.

-cat >expected <<\EOF
-:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 6ff87c4664981e4397625791c8ea3bbb5f2279a3 R100	path0/COPYING	path1/COPYING
+cat >expected <<EOF
+:100644 100644 $blob $blob R100	path0/COPYING	path1/COPYING
 EOF

 test_expect_success 'rename detection' '
@ -78,8 +79,8 @@ test_expect_success 'rename detection' '
 # path0/COPYING.  When we say we care only about path1, we should just
 # see path1/COPYING appearing from nowhere.

-cat >expected <<\EOF
-:000000 100644 0000000000000000000000000000000000000000 6ff87c4664981e4397625791c8ea3bbb5f2279a3 A	path1/COPYING
+cat >expected <<EOF
+:000000 100644 $ZERO_OID $blob A	path1/COPYING
 EOF

 test_expect_success 'rename, limited to a subtree' '
--- a/t/t4008-diff-break-rewrite.sh
+++ b/t/t4008-diff-break-rewrite.sh
@ -27,29 +27,32 @@ Further, with -B and -M together, these should turn into two renames.
 test_expect_success setup '
 	cat "$TEST_DIRECTORY"/diff-lib/README >file0 &&
 	cat "$TEST_DIRECTORY"/diff-lib/COPYING >file1 &&
+	blob0_id=$(git hash-object file0) &&
+	blob1_id=$(git hash-object file1) &&
 	git update-index --add file0 file1 &&
 	git tag reference $(git write-tree)
 '

 test_expect_success 'change file1 with copy-edit of file0 and remove file0' '
 	sed -e "s/git/GIT/" file0 >file1 &&
+	blob2_id=$(git hash-object file1) &&
 	rm -f file0 &&
 	git update-index --remove file0 file1
 '

 test_expect_success 'run diff with -B (#1)' '
 	git diff-index -B --cached reference >current &&
-	cat >expect <<-\EOF &&
-	:100644 000000 548142c327a6790ff8821d67c2ee1eff7a656b52 0000000000000000000000000000000000000000 D	file0
-	:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 2fbedd0b5d4b8126e4750c3bee305e8ff79f80ec M100	file1
+	cat >expect <<-EOF &&
+	:100644 000000 $blob0_id $ZERO_OID D	file0
+	:100644 100644 $blob1_id $blob2_id M100	file1
 	EOF
 	compare_diff_raw expect current
 '

 test_expect_success 'run diff with -B and -M (#2)' '
 	git diff-index -B -M reference >current &&
-	cat >expect <<-\EOF &&
-	:100644 100644 548142c327a6790ff8821d67c2ee1eff7a656b52 2fbedd0b5d4b8126e4750c3bee305e8ff79f80ec R100	file0	file1
+	cat >expect <<-EOF &&
+	:100644 100644 $blob0_id $blob2_id R100	file0	file1
 	EOF
 	compare_diff_raw expect current
 '
@ -66,18 +69,18 @@ test_expect_success 'swap file0 and file1' '

 test_expect_success 'run diff with -B (#3)' '
 	git diff-index -B reference >current &&
-	cat >expect <<-\EOF &&
-	:100644 100644 548142c327a6790ff8821d67c2ee1eff7a656b52 6ff87c4664981e4397625791c8ea3bbb5f2279a3 M100	file0
-	:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 548142c327a6790ff8821d67c2ee1eff7a656b52 M100	file1
+	cat >expect <<-EOF &&
+	:100644 100644 $blob0_id $blob1_id M100	file0
+	:100644 100644 $blob1_id $blob0_id M100	file1
 	EOF
 	compare_diff_raw expect current
 '

 test_expect_success 'run diff with -B and -M (#4)' '
 	git diff-index -B -M reference >current &&
-	cat >expect <<-\EOF &&
-	:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 6ff87c4664981e4397625791c8ea3bbb5f2279a3 R100	file1	file0
-	:100644 100644 548142c327a6790ff8821d67c2ee1eff7a656b52 548142c327a6790ff8821d67c2ee1eff7a656b52 R100	file0	file1
+	cat >expect <<-EOF &&
+	:100644 100644 $blob1_id $blob1_id R100	file1	file0
+	:100644 100644 $blob0_id $blob0_id R100	file0	file1
 	EOF
 	compare_diff_raw expect current
 '
@ -85,14 +88,15 @@ test_expect_success 'run diff with -B and -M (#4)' '
 test_expect_success 'make file0 into something completely different' '
 	rm -f file0 &&
 	test_ln_s_add frotz file0 &&
+	slink_id=$(printf frotz | git hash-object --stdin) &&
 	git update-index file1
 '

 test_expect_success 'run diff with -B (#5)' '
 	git diff-index -B reference >current &&
-	cat >expect <<-\EOF &&
-	:100644 120000 548142c327a6790ff8821d67c2ee1eff7a656b52 67be421f88824578857624f7b3dc75e99a8a1481 T	file0
-	:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 548142c327a6790ff8821d67c2ee1eff7a656b52 M100	file1
+	cat >expect <<-EOF &&
+	:100644 120000 $blob0_id $slink_id T	file0
+	:100644 100644 $blob1_id $blob0_id M100	file1
 	EOF
 	compare_diff_raw expect current
 '
@ -103,9 +107,9 @@ test_expect_success 'run diff with -B -M (#6)' '
 	# file0 changed from regular to symlink.  file1 is the same as the preimage
 	# of file0.  Because the change does not make file0 disappear, file1 is
 	# denoted as a copy of file0
-	cat >expect <<-\EOF &&
-	:100644 120000 548142c327a6790ff8821d67c2ee1eff7a656b52 67be421f88824578857624f7b3dc75e99a8a1481 T	file0
-	:100644 100644 548142c327a6790ff8821d67c2ee1eff7a656b52 548142c327a6790ff8821d67c2ee1eff7a656b52 C	file0	file1
+	cat >expect <<-EOF &&
+	:100644 120000 $blob0_id $slink_id T	file0
+	:100644 100644 $blob0_id $blob0_id C	file0	file1
 	EOF
 	compare_diff_raw expect current
 '
@ -115,9 +119,9 @@ test_expect_success 'run diff with -M (#7)' '

 	# This should not mistake file0 as the copy source of new file1
 	# due to type differences.
-	cat >expect <<-\EOF &&
-	:100644 120000 548142c327a6790ff8821d67c2ee1eff7a656b52 67be421f88824578857624f7b3dc75e99a8a1481 T	file0
-	:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 548142c327a6790ff8821d67c2ee1eff7a656b52 M	file1
+	cat >expect <<-EOF &&
+	:100644 120000 $blob0_id $slink_id T	file0
+	:100644 100644 $blob1_id $blob0_id M	file1
 	EOF
 	compare_diff_raw expect current
 '
@ -128,25 +132,26 @@ test_expect_success 'file1 edited to look like file0 and file0 rename-edited to
 	git checkout-index -f -u -a &&
 	sed -e "s/git/GIT/" file0 >file1 &&
 	sed -e "s/git/GET/" file0 >file2 &&
+	blob3_id=$(git hash-object file2) &&
 	rm -f file0 &&
 	git update-index --add --remove file0 file1 file2
 '

 test_expect_success 'run diff with -B (#8)' '
 	git diff-index -B reference >current &&
-	cat >expect <<-\EOF &&
-	:100644 000000 548142c327a6790ff8821d67c2ee1eff7a656b52 0000000000000000000000000000000000000000 D	file0
-	:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 2fbedd0b5d4b8126e4750c3bee305e8ff79f80ec M100	file1
-	:000000 100644 0000000000000000000000000000000000000000 69a939f651686f56322566e2fd76715947a24162 A	file2
+	cat >expect <<-EOF &&
+	:100644 000000 $blob0_id $ZERO_OID D	file0
+	:100644 100644 $blob1_id $blob2_id M100	file1
+	:000000 100644 $ZERO_OID $blob3_id A	file2
 	EOF
 	compare_diff_raw expect current
 '

 test_expect_success 'run diff with -B -C (#9)' '
 	git diff-index -B -C reference >current &&
-	cat >expect <<-\EOF &&
-	:100644 100644 548142c327a6790ff8821d67c2ee1eff7a656b52 2fbedd0b5d4b8126e4750c3bee305e8ff79f80ec C095	file0	file1
-	:100644 100644 548142c327a6790ff8821d67c2ee1eff7a656b52 69a939f651686f56322566e2fd76715947a24162 R095	file0	file2
+	cat >expect <<-EOF &&
+	:100644 100644 $blob0_id $blob2_id C095	file0	file1
+	:100644 100644 $blob0_id $blob3_id R095	file0	file2
 	EOF
 	compare_diff_raw expect current
 '
--- a/t/t4014-format-patch.sh
+++ b/t/t4014-format-patch.sh
@ -578,7 +578,11 @@ test_expect_success 'excessive subject' '

 	rm -rf patches/ &&
 	git checkout side &&
+	before=$(git hash-object file) &&
+	before=$(git rev-parse --short $before) &&
 	for i in 5 6 1 2 3 A 4 B C 7 8 9 10 D E F; do echo "$i"; done >>file &&
+	after=$(git hash-object file) &&
+	after=$(git rev-parse --short $after) &&
 	git update-index file &&
 	git commit -m "This is an excessively long subject line for a message due to the habit some projects have of not having a short, one-line subject at the start of the commit message, but rather sticking a whole paragraph right at the start as the only thing in the commit message. It had better not become the filename for the patch." &&
 	git format-patch -o patches/ master..side &&
@ -586,7 +590,6 @@ test_expect_success 'excessive subject' '
 '

 test_expect_success 'cover-letter inherits diff options' '
-
 	git mv file foo &&
 	git commit -m foo &&
 	git format-patch --no-renames --cover-letter -1 &&
@ -616,7 +619,7 @@ test_expect_success 'shortlog of cover-letter wraps overly-long onelines' '
 '

 cat > expect << EOF
-index 40f36c6..2dc5c23 100644
+index $before..$after 100644
 --- a/file
 +++ b/file
@@ -13,4 +13,20 @@ C
@ -640,7 +643,7 @@ test_expect_success 'format-patch respects -U' '
 cat > expect << EOF

 diff --git a/file b/file
-index 40f36c6..2dc5c23 100644
+index $before..$after 100644
 --- a/file
 +++ b/file
@@ -14,3 +14,19 @@ C
@ -1523,14 +1526,14 @@ test_expect_success 'cover letter auto user override' '
 test_expect_success 'format-patch --zero-commit' '
 	git format-patch --zero-commit --stdout v2..v1 >patch2 &&
 	grep "^From " patch2 | sort | uniq >actual &&
-	echo "From $_z40 Mon Sep 17 00:00:00 2001" >expect &&
+	echo "From $ZERO_OID Mon Sep 17 00:00:00 2001" >expect &&
 	test_cmp expect actual
 '

 test_expect_success 'From line has expected format' '
 	git format-patch --stdout v2..v1 >patch2 &&
 	grep "^From " patch2 >from &&
-	grep "^From $_x40 Mon Sep 17 00:00:00 2001$" patch2 >filtered &&
+	grep "^From $OID_REGEX Mon Sep 17 00:00:00 2001$" patch2 >filtered &&
 	test_cmp from filtered
 '

--- a/t/t4020-diff-external.sh
+++ b/t/t4020-diff-external.sh
@ -13,6 +13,8 @@ test_expect_success setup '

 	test_tick &&
 	echo second >file &&
+	before=$(git hash-object file) &&
+	before=$(git rev-parse --short $before) &&
 	git add file &&
 	git commit -m second &&

@ -26,7 +28,7 @@ test_expect_success 'GIT_EXTERNAL_DIFF environment' '
 		read path oldfile oldhex oldmode newfile newhex newmode &&
 		test "z$path" = zfile &&
 		test "z$oldmode" = z100644 &&
-		test "z$newhex" = "z$_z40" &&
+		test "z$newhex" = "z$ZERO_OID" &&
 		test "z$newmode" = z100644 &&
 		oh=$(git rev-parse --verify HEAD:file) &&
 		test "z$oh" = "z$oldhex"
@ -55,7 +57,7 @@ test_expect_success SYMLINKS 'typechange diff' '
 		read path oldfile oldhex oldmode newfile newhex newmode &&
 		test "z$path" = zfile &&
 		test "z$oldmode" = z100644 &&
-		test "z$newhex" = "z$_z40" &&
+		test "z$newhex" = "z$ZERO_OID" &&
 		test "z$newmode" = z120000 &&
 		oh=$(git rev-parse --verify HEAD:file) &&
 		test "z$oh" = "z$oldhex"
@ -73,7 +75,7 @@ test_expect_success 'diff.external' '
 		read path oldfile oldhex oldmode newfile newhex newmode &&
 		test "z$path" = zfile &&
 		test "z$oldmode" = z100644 &&
-		test "z$newhex" = "z$_z40" &&
+		test "z$newhex" = "z$ZERO_OID" &&
 		test "z$newmode" = z100644 &&
 		oh=$(git rev-parse --verify HEAD:file) &&
 		test "z$oh" = "z$oldhex"
@ -104,7 +106,7 @@ test_expect_success 'diff attribute' '
 		read path oldfile oldhex oldmode newfile newhex newmode &&
 		test "z$path" = zfile &&
 		test "z$oldmode" = z100644 &&
-		test "z$newhex" = "z$_z40" &&
+		test "z$newhex" = "z$ZERO_OID" &&
 		test "z$newmode" = z100644 &&
 		oh=$(git rev-parse --verify HEAD:file) &&
 		test "z$oh" = "z$oldhex"
@ -137,7 +139,7 @@ test_expect_success 'diff attribute' '
 		read path oldfile oldhex oldmode newfile newhex newmode &&
 		test "z$path" = zfile &&
 		test "z$oldmode" = z100644 &&
-		test "z$newhex" = "z$_z40" &&
+		test "z$newhex" = "z$ZERO_OID" &&
 		test "z$newmode" = z100644 &&
 		oh=$(git rev-parse --verify HEAD:file) &&
 		test "z$oh" = "z$oldhex"
@ -180,9 +182,13 @@ test_expect_success 'no diff with -diff' '
 echo NULZbetweenZwords | perl -pe 'y/Z/\000/' > file

 test_expect_success 'force diff with "diff"' '
+	after=$(git hash-object file) &&
+	after=$(git rev-parse --short $after) &&
 	echo >.gitattributes "file diff" &&
 	git diff >actual &&
-	test_cmp "$TEST_DIRECTORY"/t4020/diff.NUL actual
+	sed -e "s/^index .*/index $before..$after 100644/" \
+		"$TEST_DIRECTORY"/t4020/diff.NUL >expected-diff &&
+	test_cmp expected-diff actual
 '

 test_expect_success 'GIT_EXTERNAL_DIFF with more than one changed files' '
@ -237,7 +243,7 @@ test_expect_success 'diff --cached' '
 	git update-index --assume-unchanged file &&
 	echo second >file &&
 	git diff --cached >actual &&
-	test_cmp "$TEST_DIRECTORY"/t4020/diff.NUL actual
+	test_cmp expected-diff actual
 '

 test_expect_success 'clean up crlf leftovers' '
--- a/t/t4022-diff-rewrite.sh
+++ b/t/t4022-diff-rewrite.sh
@ -13,6 +13,8 @@ test_expect_success setup '
 	  "nopqrstuvwxyzabcdefghijklmNOPQRSTUVWXYZABCDEFGHIJKLM" \
 	  <"$TEST_DIRECTORY"/../COPYING >test &&
 	echo "to be deleted" >test2 &&
+	blob=$(git hash-object test2) &&
+	blob=$(git rev-parse --short $blob) &&
 	git add test2

 '
@ -27,7 +29,7 @@ test_expect_success 'detect rewrite' '
 cat >expect <<EOF
 diff --git a/test2 b/test2
 deleted file mode 100644
-index 4202011..0000000
+index $blob..0000000
 --- a/test2
 +++ /dev/null
@@ -1 +0,0 @@
@ -43,7 +45,7 @@ test_expect_success 'show deletion diff without -D' '
 cat >expect <<EOF
 diff --git a/test2 b/test2
 deleted file mode 100644
-index 4202011..0000000
+index $blob..0000000
 EOF
 test_expect_success 'suppress deletion diff with -D' '

--- a/t/t4027-diff-submodule.sh
+++ b/t/t4027-diff-submodule.sh
@ -31,7 +31,7 @@ test_expect_success setup '
 		cd sub &&
 		git rev-list HEAD
 	) &&
-	echo ":160000 160000 $3 $_z40 M	sub" >expect &&
+	echo ":160000 160000 $3 $ZERO_OID M	sub" >expect &&
 	subtip=$3 subprev=$2
 '

@ -250,7 +250,7 @@ test_expect_success 'conflicted submodule setup' '
 	# 39 efs
 	c=fffffffffffffffffffffffffffffffffffffff &&
 	(
-		echo "000000 $_z40 0	sub" &&
+		echo "000000 $ZERO_OID 0	sub" &&
 		echo "160000 1$c 1	sub" &&
 		echo "160000 2$c 2	sub" &&
 		echo "160000 3$c 3	sub"
@ -265,7 +265,7 @@ index 2ffffff,3ffffff..0000000
 ++Subproject commit 0000000000000000000000000000000000000000'\'' &&

 	hh=$(git rev-parse HEAD) &&
-	sed -e "s/$_z40/$hh/" expect.nosub >expect.withsub
+	sed -e "s/$ZERO_OID/$hh/" expect.nosub >expect.withsub

 '

--- a/t/t4029-diff-trailing-space.sh
+++ b/t/t4029-diff-trailing-space.sh
@ -6,7 +6,7 @@ test_description='diff honors config option, diff.suppressBlankEmpty'

 . ./test-lib.sh

-cat <<\EOF > exp ||
+cat <<\EOF >expected ||
 diff --git a/f b/f
 index 5f6a263..8cb8bae 100644
 --- a/f
@ -18,22 +18,26 @@ index 5f6a263..8cb8bae 100644
 EOF
 exit 1

-test_expect_success \
-    "$test_description" \
-    'printf "\nx\n" > f &&
-     git add f &&
-     git commit -q -m. f &&
-     printf "\ny\n" > f &&
-     git config --bool diff.suppressBlankEmpty true &&
-     git diff f > actual &&
-     test_cmp exp actual &&
-     perl -i.bak -p -e "s/^\$/ /" exp &&
-     git config --bool diff.suppressBlankEmpty false &&
-     git diff f > actual &&
-     test_cmp exp actual &&
-     git config --bool --unset diff.suppressBlankEmpty &&
-     git diff f > actual &&
-     test_cmp exp actual
-     '
+test_expect_success "$test_description" '
+	printf "\nx\n" > f &&
+	before=$(git hash-object f) &&
+	before=$(git rev-parse --short $before) &&
+	git add f &&
+	git commit -q -m. f &&
+	printf "\ny\n" > f &&
+	after=$(git hash-object f) &&
+	after=$(git rev-parse --short $after) &&
+	sed -e "s/^index .*/index $before..$after 100644/" expected >exp &&
+	git config --bool diff.suppressBlankEmpty true &&
+	git diff f > actual &&
+	test_cmp exp actual &&
+	perl -i.bak -p -e "s/^\$/ /" exp &&
+	git config --bool diff.suppressBlankEmpty false &&
+	git diff f > actual &&
+	test_cmp exp actual &&
+	git config --bool --unset diff.suppressBlankEmpty &&
+	git diff f > actual &&
+	test_cmp exp actual
+'

 test_done
--- a/t/t4030-diff-textconv.sh
+++ b/t/t4030-diff-textconv.sh
@ -148,7 +148,8 @@ test_expect_success 'diffstat does not run textconv' '
 # restore working setup
 echo file diff=foo >.gitattributes

-cat >expect.typechange <<'EOF'
+symlink=$(git rev-parse --short $(printf frotz | git hash-object --stdin))
+cat >expect.typechange <<EOF
 --- a/file
 +++ /dev/null
@@ -1,2 +0,0 @@
@ -156,7 +157,7 @@ cat >expect.typechange <<'EOF'
 -1
 diff --git a/file b/file
 new file mode 120000
-index 0000000..67be421
+index 0000000..$symlink
 --- /dev/null
 +++ b/file
@@ -0,0 +1 @@
--- a/t/t4042-diff-textconv-caching.sh
+++ b/t/t4042-diff-textconv-caching.sh
@ -15,9 +15,13 @@ test_expect_success 'setup' '
 	echo bar content 1 >bar.bin &&
 	git add . &&
 	git commit -m one &&
+	foo1=$(git rev-parse --short HEAD:foo.bin) &&
+	bar1=$(git rev-parse --short HEAD:bar.bin) &&
 	echo foo content 2 >foo.bin &&
 	echo bar content 2 >bar.bin &&
 	git commit -a -m two &&
+	foo2=$(git rev-parse --short HEAD:foo.bin) &&
+	bar2=$(git rev-parse --short HEAD:bar.bin) &&
 	echo "*.bin diff=magic" >.gitattributes &&
 	git config diff.magic.textconv ./helper &&
 	git config diff.magic.cachetextconv true
@ -25,14 +29,14 @@ test_expect_success 'setup' '

 cat >expect <<EOF
 diff --git a/bar.bin b/bar.bin
-index fcf9166..28283d5 100644
+index $bar1..$bar2 100644
 --- a/bar.bin
 +++ b/bar.bin
@@ -1 +1 @@
 -converted: bar content 1
 +converted: bar content 2
 diff --git a/foo.bin b/foo.bin
-index d5b9fe3..1345db2 100644
+index $foo1..$foo2 100644
 --- a/foo.bin
 +++ b/foo.bin
@@ -1 +1 @@
@ -59,7 +63,7 @@ test_expect_success 'cached textconv does not run helper' '

 cat >expect <<EOF
 diff --git a/bar.bin b/bar.bin
-index fcf9166..28283d5 100644
+index $bar1..$bar2 100644
 --- a/bar.bin
 +++ b/bar.bin
@@ -1,2 +1,2 @@
@ -67,7 +71,7 @@ index fcf9166..28283d5 100644
 -converted: bar content 1
 +converted: bar content 2
 diff --git a/foo.bin b/foo.bin
-index d5b9fe3..1345db2 100644
+index $foo1..$foo2 100644
 --- a/foo.bin
 +++ b/foo.bin
@@ -1,2 +1,2 @@
@ -84,7 +88,7 @@ test_expect_success 'changing textconv invalidates cache' '

 cat >expect <<EOF
 diff --git a/bar.bin b/bar.bin
-index fcf9166..28283d5 100644
+index $bar1..$bar2 100644
 --- a/bar.bin
 +++ b/bar.bin
@@ -1,2 +1,2 @@
@ -92,7 +96,7 @@ index fcf9166..28283d5 100644
 -converted: bar content 1
 +converted: bar content 2
 diff --git a/foo.bin b/foo.bin
-index d5b9fe3..1345db2 100644
+index $foo1..$foo2 100644
 --- a/foo.bin
 +++ b/foo.bin
@@ -1 +1 @@
--- a/t/t4044-diff-index-unique-abbrev.sh
+++ b/t/t4044-diff-index-unique-abbrev.sh
@ -3,6 +3,12 @@
 test_description='test unique sha1 abbreviation on "index from..to" line'
 . ./test-lib.sh

+if ! test_have_prereq SHA1
+then
+       skip_all='not using SHA-1 for objects'
+       test_done
+fi
+
 cat >expect_initial <<EOF
 100644 blob 51d2738463ea4ca66f8691c91e33ce64b7d41bb1	foo
 EOF
--- a/t/t4045-diff-relative.sh
+++ b/t/t4045-diff-relative.sh
@ -8,6 +8,7 @@ test_expect_success 'setup' '
 	echo content >file1 &&
 	mkdir subdir &&
 	echo other content >subdir/file2 &&
+	blob=$(git hash-object subdir/file2) &&
 	git add . &&
 	git commit -m one
 '
@ -17,10 +18,11 @@ check_diff () {
 	shift
 	expect=$1
 	shift
+	short_blob=$(git rev-parse --short $blob)
 	cat >expected <<-EOF
 	diff --git a/$expect b/$expect
 	new file mode 100644
-	index 0000000..25c05ef
+	index 0000000..$short_blob
 	--- /dev/null
 	+++ b/$expect
 	@@ -0,0 +1 @@
@ -68,7 +70,7 @@ check_raw () {
 	expect=$1
 	shift
 	cat >expected <<-EOF
-	:000000 100644 0000000000000000000000000000000000000000 25c05ef3639d2d270e7fe765a67668f098092bc5 A	$expect
+	:000000 100644 0000000000000000000000000000000000000000 $blob A	$expect
 	EOF
 	test_expect_success "--raw $*" "
 		git -C '$dir' diff --no-abbrev --raw $* HEAD^ >actual &&
--- a/t/t4046-diff-unmerged.sh
+++ b/t/t4046-diff-unmerged.sh
@ -37,7 +37,7 @@ test_expect_success 'diff-files -0' '
 	for path in $paths
 	do
 		>"$path" &&
-		echo ":000000 100644 $_z40 $_z40 U	$path"
+		echo ":000000 100644 $ZERO_OID $ZERO_OID U	$path"
 	done >diff-files-0.expect &&
 	git diff-files -0 >diff-files-0.actual &&
 	test_cmp diff-files-0.expect diff-files-0.actual
@ -47,9 +47,9 @@ test_expect_success 'diff-files -1' '
 	for path in $paths
 	do
 		>"$path" &&
-		echo ":000000 100644 $_z40 $_z40 U	$path" &&
+		echo ":000000 100644 $ZERO_OID $ZERO_OID U	$path" &&
 		case "$path" in
-		x??) echo ":100644 100644 $blob1 $_z40 M	$path"
+		x??) echo ":100644 100644 $blob1 $ZERO_OID M	$path"
 		esac
 	done >diff-files-1.expect &&
 	git diff-files -1 >diff-files-1.actual &&
@ -60,9 +60,9 @@ test_expect_success 'diff-files -2' '
 	for path in $paths
 	do
 		>"$path" &&
-		echo ":000000 100644 $_z40 $_z40 U	$path" &&
+		echo ":000000 100644 $ZERO_OID $ZERO_OID U	$path" &&
 		case "$path" in
-		?x?) echo ":100644 100644 $blob2 $_z40 M	$path"
+		?x?) echo ":100644 100644 $blob2 $ZERO_OID M	$path"
 		esac
 	done >diff-files-2.expect &&
 	git diff-files -2 >diff-files-2.actual &&
@ -75,9 +75,9 @@ test_expect_success 'diff-files -3' '
 	for path in $paths
 	do
 		>"$path" &&
-		echo ":000000 100644 $_z40 $_z40 U	$path" &&
+		echo ":000000 100644 $ZERO_OID $ZERO_OID U	$path" &&
 		case "$path" in
-		??x) echo ":100644 100644 $blob3 $_z40 M	$path"
+		??x) echo ":100644 100644 $blob3 $ZERO_OID M	$path"
 		esac
 	done >diff-files-3.expect &&
 	git diff-files -3 >diff-files-3.actual &&
--- a/t/t4054-diff-bogus-tree.sh
+++ b/t/t4054-diff-bogus-tree.sh
@ -19,37 +19,37 @@ test_expect_success 'create tree with matching file' '
 '

 test_expect_success 'raw diff shows null sha1 (addition)' '
-	echo ":000000 100644 $_z40 $_z40 A	foo" >expect &&
+	echo ":000000 100644 $ZERO_OID $ZERO_OID A	foo" >expect &&
 	git diff-tree $EMPTY_TREE $bogus_tree >actual &&
 	test_cmp expect actual
 '

 test_expect_success 'raw diff shows null sha1 (removal)' '
-	echo ":100644 000000 $_z40 $_z40 D	foo" >expect &&
+	echo ":100644 000000 $ZERO_OID $ZERO_OID D	foo" >expect &&
 	git diff-tree $bogus_tree $EMPTY_TREE >actual &&
 	test_cmp expect actual
 '

 test_expect_success 'raw diff shows null sha1 (modification)' '
-	echo ":100644 100644 $blob $_z40 M	foo" >expect &&
+	echo ":100644 100644 $blob $ZERO_OID M	foo" >expect &&
 	git diff-tree $good_tree $bogus_tree >actual &&
 	test_cmp expect actual
 '

 test_expect_success 'raw diff shows null sha1 (other direction)' '
-	echo ":100644 100644 $_z40 $blob M	foo" >expect &&
+	echo ":100644 100644 $ZERO_OID $blob M	foo" >expect &&
 	git diff-tree $bogus_tree $good_tree >actual &&
 	test_cmp expect actual
 '

 test_expect_success 'raw diff shows null sha1 (reverse)' '
-	echo ":100644 100644 $_z40 $blob M	foo" >expect &&
+	echo ":100644 100644 $ZERO_OID $blob M	foo" >expect &&
 	git diff-tree -R $good_tree $bogus_tree >actual &&
 	test_cmp expect actual
 '

 test_expect_success 'raw diff shows null sha1 (index)' '
-	echo ":100644 100644 $_z40 $blob M	foo" >expect &&
+	echo ":100644 100644 $ZERO_OID $blob M	foo" >expect &&
 	git diff-index $bogus_tree >actual &&
 	test_cmp expect actual
 '
--- a/t/t4058-diff-duplicates.sh
+++ b/t/t4058-diff-duplicates.sh
@ -59,12 +59,12 @@ test_expect_success 'create trees with duplicate entries' '

 test_expect_success 'diff-tree between trees' '
 	{
-		printf ":000000 100644 $_z40 $blob_two A\touter/inner\n" &&
-		printf ":000000 100644 $_z40 $blob_two A\touter/inner\n" &&
-		printf ":000000 100644 $_z40 $blob_two A\touter/inner\n" &&
-		printf ":100644 000000 $blob_two $_z40 D\touter/inner\n" &&
-		printf ":100644 000000 $blob_two $_z40 D\touter/inner\n" &&
-		printf ":100644 000000 $blob_two $_z40 D\touter/inner\n"
+		printf ":000000 100644 $ZERO_OID $blob_two A\touter/inner\n" &&
+		printf ":000000 100644 $ZERO_OID $blob_two A\touter/inner\n" &&
+		printf ":000000 100644 $ZERO_OID $blob_two A\touter/inner\n" &&
+		printf ":100644 000000 $blob_two $ZERO_OID D\touter/inner\n" &&
+		printf ":100644 000000 $blob_two $ZERO_OID D\touter/inner\n" &&
+		printf ":100644 000000 $blob_two $ZERO_OID D\touter/inner\n"
 	} >expect &&
 	git diff-tree -r --no-abbrev one two >actual &&
 	test_cmp expect actual
--- a/t/t4150-am.sh
+++ b/t/t4150-am.sh
@ -140,8 +140,8 @@ test_expect_success setup '
 		echo "# User $GIT_AUTHOR_NAME <$GIT_AUTHOR_EMAIL>" &&
 		echo "# Date $test_tick 25200" &&
 		echo "#      $(git show --pretty="%aD" -s second)" &&
-		echo "# Node ID $_z40" &&
-		echo "# Parent  $_z40" &&
+		echo "# Node ID $ZERO_OID" &&
+		echo "# Parent  $ZERO_OID" &&
 		cat msg &&
 		echo &&
 		git diff-tree --no-commit-id -p second
--- a/t/t4200-rerere.sh
+++ b/t/t4200-rerere.sh
@ -243,7 +243,7 @@ rerere_gc_custom_expiry_test () {
 	five_days="$1" right_now="$2"
 	test_expect_success "rerere gc with custom expiry ($five_days, $right_now)" '
 		rm -fr .git/rr-cache &&
-		rr=.git/rr-cache/$_z40 &&
+		rr=.git/rr-cache/$ZERO_OID &&
 		mkdir -p "$rr" &&
 		>"$rr/preimage" &&
 		>"$rr/postimage" &&
--- a/t/t4201-shortlog.sh
+++ b/t/t4201-shortlog.sh
@ -59,7 +59,7 @@ test_expect_success 'setup' '
 fuzz() {
 	file=$1 &&
 	sed "
-			s/$_x40/OBJECT_NAME/g
+			s/$OID_REGEX/OBJECT_NAME/g
 			s/$_x35/OBJID/g
 			s/^ \{6\}[CTa].*/      SUBJECT/g
 			s/^ \{8\}[^ ].*/        CONTINUATION/g
--- a/t/t4205-log-pretty-formats.sh
+++ b/t/t4205-log-pretty-formats.sh
@ -516,22 +516,22 @@ test_expect_success 'log decoration properly follows tag chain' '
 	git commit --amend -m shorter &&
 	git log --no-walk --tags --pretty="%H %d" --decorate=full >actual &&
 	cat <<-EOF >expected &&
-	$head1  (tag: refs/tags/tag2)
 	$head2  (tag: refs/tags/message-one)
 	$old_head1  (tag: refs/tags/message-two)
+	$head1  (tag: refs/tags/tag2)
 	EOF
-	sort actual >actual1 &&
+	sort -k3 actual >actual1 &&
 	test_cmp expected actual1
 '

 test_expect_success 'clean log decoration' '
 	git log --no-walk --tags --pretty="%H %D" --decorate=full >actual &&
 	cat >expected <<-EOF &&
-	$head1 tag: refs/tags/tag2
 	$head2 tag: refs/tags/message-one
 	$old_head1 tag: refs/tags/message-two
+	$head1 tag: refs/tags/tag2
 	EOF
-	sort actual >actual1 &&
+	sort -k3 actual >actual1 &&
 	test_cmp expected actual1
 '

--- a/t/t4208-log-magic-pathspec.sh
+++ b/t/t4208-log-magic-pathspec.sh
@ -45,8 +45,9 @@ test_expect_success 'git log -- :' '
 '

 test_expect_success 'git log HEAD -- :/' '
+	initial=$(git rev-parse --short HEAD^) &&
 	cat >expected <<-EOF &&
-	24b24cf initial
+	$initial initial
 	EOF
 	(cd sub && git log --oneline HEAD -- :/ >../actual) &&
 	test_cmp expected actual
--- a/t/t5150-request-pull.sh
+++ b/t/t5150-request-pull.sh
@ -81,7 +81,7 @@ test_expect_success 'setup: two scripts for reading pull requests' '
 	cat <<-EOT >fuzz.sed
 	#!/bin/sed -nf
 	s/$downstream_url_for_sed/URL/g
-	s/$_x40/OBJECT_NAME/g
+	s/$OID_REGEX/OBJECT_NAME/g
 	s/A U Thor/AUTHOR/g
 	s/[-0-9]\{10\} [:0-9]\{8\} [-+][0-9]\{4\}/DATE/g
 	s/        [^ ].*/        SUBJECT/g
--- a/t/t5300-pack-object.sh
+++ b/t/t5300-pack-object.sh
@ -471,9 +471,11 @@ test_expect_success 'pack-objects in too-many-packs mode' '

 test_expect_success \
    'fake a SHA1 hash collision' \
-    'test -f	.git/objects/c8/2de19312b6c3695c0c18f70709a6c535682a67 &&
-     cp -f	.git/objects/9d/235ed07cd19811a6ceb342de82f190e49c9f68 \
-		.git/objects/c8/2de19312b6c3695c0c18f70709a6c535682a67'
+    '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 \
    'make sure index-pack detects the SHA1 collision' \
--- a/t/t5308-pack-detect-duplicates.sh
+++ b/t/t5308-pack-detect-duplicates.sh
@ -4,6 +4,12 @@ test_description='handling of duplicate objects in incoming packfiles'
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-pack.sh

+if ! test_have_prereq SHA1
+then
+       skip_all='not using SHA-1 for objects'
+       test_done
+fi
+
 # The sha1s we have in our pack. It's important that these have the same
 # starting byte, so that they end up in the same fanout section of the index.
 # That lets us make sure we are exercising the binary search with both sets.
--- a/t/t5309-pack-delta-cycles.sh
+++ b/t/t5309-pack-delta-cycles.sh
@ -4,6 +4,12 @@ test_description='test index-pack handling of delta cycles in packfiles'
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-pack.sh

+if ! test_have_prereq SHA1
+then
+       skip_all='not using SHA-1 for objects'
+       test_done
+fi
+
 # Two similar-ish objects that we have computed deltas between.
 A=01d7713666f4de822776c7622c10f1b07de280dc
 B=e68fe8129b546b101aee9510c5328e7f21ca1d18
--- a/t/t5516-fetch-push.sh
+++ b/t/t5516-fetch-push.sh
@ -634,7 +634,7 @@ test_expect_success 'pushing valid refs triggers post-receive and post-update ho
 	orgmaster=$(cd testrepo && git show-ref -s --verify refs/heads/master) &&
 	newmaster=$(git show-ref -s --verify refs/heads/master) &&
 	orgnext=$(cd testrepo && git show-ref -s --verify refs/heads/next) &&
-	newnext=$_z40 &&
+	newnext=$ZERO_OID &&
 	git push testrepo refs/heads/master:refs/heads/master :refs/heads/next &&
 	(
 		cd testrepo/.git &&
@ -672,15 +672,15 @@ test_expect_success 'deleting dangling ref triggers hooks with correct args' '
 	(
 		cd testrepo/.git &&
 		cat >pre-receive.expect <<-EOF &&
-		$_z40 $_z40 refs/heads/master
+		$ZERO_OID $ZERO_OID refs/heads/master
 		EOF

 		cat >update.expect <<-EOF &&
-		refs/heads/master $_z40 $_z40
+		refs/heads/master $ZERO_OID $ZERO_OID
 		EOF

 		cat >post-receive.expect <<-EOF &&
-		$_z40 $_z40 refs/heads/master
+		$ZERO_OID $ZERO_OID refs/heads/master
 		EOF

 		cat >post-update.expect <<-EOF &&
@ -703,12 +703,12 @@ test_expect_success 'deletion of a non-existent ref is not fed to post-receive a
 		cd testrepo/.git &&
 		cat >pre-receive.expect <<-EOF &&
 		$orgmaster $newmaster refs/heads/master
-		$_z40 $_z40 refs/heads/nonexistent
+		$ZERO_OID $ZERO_OID refs/heads/nonexistent
 		EOF

 		cat >update.expect <<-EOF &&
 		refs/heads/master $orgmaster $newmaster
-		refs/heads/nonexistent $_z40 $_z40
+		refs/heads/nonexistent $ZERO_OID $ZERO_OID
 		EOF

 		cat >post-receive.expect <<-EOF &&
@ -732,11 +732,11 @@ test_expect_success 'deletion of a non-existent ref alone does trigger post-rece
 	(
 		cd testrepo/.git &&
 		cat >pre-receive.expect <<-EOF &&
-		$_z40 $_z40 refs/heads/nonexistent
+		$ZERO_OID $ZERO_OID refs/heads/nonexistent
 		EOF

 		cat >update.expect <<-EOF &&
-		refs/heads/nonexistent $_z40 $_z40
+		refs/heads/nonexistent $ZERO_OID $ZERO_OID
 		EOF

 		test_cmp pre-receive.expect pre-receive.actual &&
@ -751,7 +751,7 @@ test_expect_success 'mixed ref updates, deletes, invalid deletes trigger hooks w
 	orgmaster=$(cd testrepo && git show-ref -s --verify refs/heads/master) &&
 	newmaster=$(git show-ref -s --verify refs/heads/master) &&
 	orgnext=$(cd testrepo && git show-ref -s --verify refs/heads/next) &&
-	newnext=$_z40 &&
+	newnext=$ZERO_OID &&
 	orgpu=$(cd testrepo && git show-ref -s --verify refs/heads/pu) &&
 	newpu=$(git show-ref -s --verify refs/heads/master) &&
 	git push testrepo refs/heads/master:refs/heads/master \
@ -763,14 +763,14 @@ test_expect_success 'mixed ref updates, deletes, invalid deletes trigger hooks w
 		$orgmaster $newmaster refs/heads/master
 		$orgnext $newnext refs/heads/next
 		$orgpu $newpu refs/heads/pu
-		$_z40 $_z40 refs/heads/nonexistent
+		$ZERO_OID $ZERO_OID refs/heads/nonexistent
 		EOF

 		cat >update.expect <<-EOF &&
 		refs/heads/master $orgmaster $newmaster
 		refs/heads/next $orgnext $newnext
 		refs/heads/pu $orgpu $newpu
-		refs/heads/nonexistent $_z40 $_z40
+		refs/heads/nonexistent $ZERO_OID $ZERO_OID
 		EOF

 		cat >post-receive.expect <<-EOF &&
--- a/t/t5527-fetch-odd-refs.sh
+++ b/t/t5527-fetch-odd-refs.sh
@ -27,7 +27,7 @@ test_expect_success 'suffix ref is ignored during fetch' '
 '

 test_expect_success 'try to create repo with absurdly long refname' '
-	ref240=$_z40/$_z40/$_z40/$_z40/$_z40/$_z40 &&
+	ref240=$ZERO_OID/$ZERO_OID/$ZERO_OID/$ZERO_OID/$ZERO_OID/$ZERO_OID &&
 	ref1440=$ref240/$ref240/$ref240/$ref240/$ref240/$ref240 &&
 	git init long &&
 	(
--- a/t/t5571-pre-push-hook.sh
+++ b/t/t5571-pre-push-hook.sh
@ -78,8 +78,8 @@ test_expect_success 'push to default' '
 cat >expected <<EOF
 parent1
 repo1
-refs/tags/one $COMMIT1 refs/tags/tag1 $_z40
-HEAD~ $COMMIT2 refs/heads/prev $_z40
+refs/tags/one $COMMIT1 refs/tags/tag1 $ZERO_OID
+HEAD~ $COMMIT2 refs/heads/prev $ZERO_OID
 EOF

 test_expect_success 'push non-branches' '
@ -90,7 +90,7 @@ test_expect_success 'push non-branches' '
 cat >expected <<EOF
 parent1
 repo1
-(delete) $_z40 refs/heads/prev $COMMIT2
+(delete) $ZERO_OID refs/heads/prev $COMMIT2
 EOF

 test_expect_success 'push delete' '
@ -101,7 +101,7 @@ test_expect_success 'push delete' '
 cat >expected <<EOF
 repo1
 repo1
-HEAD $COMMIT3 refs/heads/other $_z40
+HEAD $COMMIT3 refs/heads/other $ZERO_OID
 EOF

 test_expect_success 'push to URL' '
--- a/t/t6006-rev-list-format.sh
+++ b/t/t6006-rev-list-format.sh
@ -447,8 +447,8 @@ test_expect_success '--abbrev' '
 	git log -1 --format="%h %h %h" HEAD >actual1 &&
 	git log -1 --abbrev=5 --format="%h %h %h" HEAD >actual2 &&
 	git log -1 --abbrev=5 --format="%H %H %H" HEAD >actual3 &&
-	sed -e "s/$_x40/LONG/g" -e "s/$_x05/SHORT/g" <actual2 >fuzzy2 &&
-	sed -e "s/$_x40/LONG/g" -e "s/$_x05/SHORT/g" <actual3 >fuzzy3 &&
+	sed -e "s/$OID_REGEX/LONG/g" -e "s/$_x05/SHORT/g" <actual2 >fuzzy2 &&
+	sed -e "s/$OID_REGEX/LONG/g" -e "s/$_x05/SHORT/g" <actual3 >fuzzy3 &&
 	test_cmp expect2 fuzzy2 &&
 	test_cmp expect3 fuzzy3 &&
 	! test_cmp actual1 actual2
--- a/t/t6012-rev-list-simplify.sh
+++ b/t/t6012-rev-list-simplify.sh
@ -9,7 +9,7 @@ note () {
 }

 unnote () {
-	git name-rev --tags --stdin | sed -e "s|$_x40 (tags/\([^)]*\)) |\1 |g"
+	git name-rev --tags --stdin | sed -e "s|$OID_REGEX (tags/\([^)]*\)) |\1 |g"
 }

 test_expect_success setup '
--- a/t/t6111-rev-list-treesame.sh
+++ b/t/t6111-rev-list-treesame.sh
@ -20,7 +20,7 @@ note () {
 }

 unnote () {
-	git name-rev --tags --stdin | sed -e "s|$_x40 (tags/\([^)]*\))\([ 	]\)|\1\2|g"
+	git name-rev --tags --stdin | sed -e "s|$OID_REGEX (tags/\([^)]*\))\([ 	]\)|\1\2|g"
 }

 test_expect_success setup '
--- a/t/t6120-describe.sh
+++ b/t/t6120-describe.sh
@ -383,7 +383,7 @@ test_expect_success 'describe complains about tree object' '
 '

 test_expect_success 'describe complains about missing object' '
-	test_must_fail git describe $_z40
+	test_must_fail git describe $ZERO_OID
 '

 test_done
--- a/t/t6300-for-each-ref.sh
+++ b/t/t6300-for-each-ref.sh
@ -310,7 +310,7 @@ test_expect_success 'exercise strftime with odd fields' '
 	echo >expected &&
 	git for-each-ref --format="%(authordate:format:)" refs/heads >actual &&
 	test_cmp expected actual &&
-	long="long format -- $_z40$_z40$_z40$_z40$_z40$_z40$_z40" &&
+	long="long format -- $ZERO_OID$ZERO_OID$ZERO_OID$ZERO_OID$ZERO_OID$ZERO_OID$ZERO_OID" &&
 	echo $long >expected &&
 	git for-each-ref --format="%(authordate:format:$long)" refs/heads >actual &&
 	test_cmp expected actual
--- a/t/t6301-for-each-ref-errors.sh
+++ b/t/t6301-for-each-ref-errors.sh
@ -4,7 +4,7 @@ test_description='for-each-ref errors for broken refs'

 . ./test-lib.sh

-ZEROS=$_z40
+ZEROS=$ZERO_OID
 MISSING=abababababababababababababababababababab

 test_expect_success setup '
--- a/t/t7009-filter-branch-null-sha1.sh
+++ b/t/t7009-filter-branch-null-sha1.sh
@ -12,7 +12,7 @@ test_expect_success 'setup: base commits' '
 test_expect_success 'setup: a commit with a bogus null sha1 in the tree' '
 	{
 		git ls-tree HEAD &&
-		printf "160000 commit $_z40\\tbroken\\n"
+		printf "160000 commit $ZERO_OID\\tbroken\\n"
 	} >broken-tree &&
 	echo "add broken entry" >msg &&

--- a/t/t7011-skip-worktree-reading.sh
+++ b/t/t7011-skip-worktree-reading.sh
@ -118,7 +118,7 @@ test_expect_success 'grep with skip-worktree file' '
 	test "$(git grep --no-ext-grep test)" = "1:test"
 '

-echo ":000000 100644 $_z40 $EMPTY_BLOB A	1" > expected
+echo ":000000 100644 $ZERO_OID $EMPTY_BLOB A	1" > expected
 test_expect_success 'diff-index does not examine skip-worktree absent entries' '
 	setup_absent &&
 	git diff-index HEAD -- 1 > result &&
--- a/t/t7064-wtstatus-pv2.sh
+++ b/t/t7064-wtstatus-pv2.sh
@ -46,11 +46,11 @@ test_expect_success 'before initial commit, things added' '
 	cat >expect <<-EOF &&
 	# branch.oid (initial)
 	# branch.head master
-	1 A. N... 000000 100644 100644 $_z40 $OID_A dir1/file_a
-	1 A. N... 000000 100644 100644 $_z40 $OID_B dir1/file_b
-	1 A. N... 000000 100644 100644 $_z40 $OID_X file_x
-	1 A. N... 000000 100644 100644 $_z40 $OID_Y file_y
-	1 A. N... 000000 100644 100644 $_z40 $OID_Z file_z
+	1 A. N... 000000 100644 100644 $ZERO_OID $OID_A dir1/file_a
+	1 A. N... 000000 100644 100644 $ZERO_OID $OID_B dir1/file_b
+	1 A. N... 000000 100644 100644 $ZERO_OID $OID_X file_x
+	1 A. N... 000000 100644 100644 $ZERO_OID $OID_Y file_y
+	1 A. N... 000000 100644 100644 $ZERO_OID $OID_Z file_z
 	? actual
 	? expect
 	EOF
@ -63,11 +63,11 @@ test_expect_success 'before initial commit, things added (-z)' '
 	lf_to_nul >expect <<-EOF &&
 	# branch.oid (initial)
 	# branch.head master
-	1 A. N... 000000 100644 100644 $_z40 $OID_A dir1/file_a
-	1 A. N... 000000 100644 100644 $_z40 $OID_B dir1/file_b
-	1 A. N... 000000 100644 100644 $_z40 $OID_X file_x
-	1 A. N... 000000 100644 100644 $_z40 $OID_Y file_y
-	1 A. N... 000000 100644 100644 $_z40 $OID_Z file_z
+	1 A. N... 000000 100644 100644 $ZERO_OID $OID_A dir1/file_a
+	1 A. N... 000000 100644 100644 $ZERO_OID $OID_B dir1/file_b
+	1 A. N... 000000 100644 100644 $ZERO_OID $OID_X file_x
+	1 A. N... 000000 100644 100644 $ZERO_OID $OID_Y file_y
+	1 A. N... 000000 100644 100644 $ZERO_OID $OID_Z file_z
 	? actual
 	? expect
 	EOF
@ -128,7 +128,7 @@ test_expect_success 'after first commit, stage existing changes' '
 	# branch.oid $H0
 	# branch.head master
 	1 M. N... 100644 100644 100644 $OID_X $OID_X1 file_x
-	1 D. N... 100644 000000 000000 $OID_Z $_z40 file_z
+	1 D. N... 100644 000000 000000 $OID_Z $ZERO_OID file_z
 	? actual
 	? expect
 	EOF
@ -145,7 +145,7 @@ test_expect_success 'rename causes 2 path lines' '
 	# branch.oid $H0
 	# branch.head master
 	1 M. N... 100644 100644 100644 $OID_X $OID_X1 file_x
-	1 D. N... 100644 000000 000000 $OID_Z $_z40 file_z
+	1 D. N... 100644 000000 000000 $OID_Z $ZERO_OID file_z
 	2 R. N... 100644 100644 100644 $OID_Y $OID_Y R100 renamed_yQfile_y
 	? actual
 	? expect
@ -163,7 +163,7 @@ test_expect_success 'rename causes 2 path lines (-z)' '
 	# branch.oid $H0
 	# branch.head master
 	1 M. N... 100644 100644 100644 $OID_X $OID_X1 file_x
-	1 D. N... 100644 000000 000000 $OID_Z $_z40 file_z
+	1 D. N... 100644 000000 000000 $OID_Z $ZERO_OID file_z
 	2 R. N... 100644 100644 100644 $OID_Y $OID_Y R100 renamed_yQfile_y
 	? actual
 	? expect
@ -246,8 +246,8 @@ test_expect_success 'verify --intent-to-add output' '
 	git add --intent-to-add intent1.add intent2.add &&

 	cat >expect <<-EOF &&
-	1 .A N... 000000 000000 100644 $_z40 $_z40 intent1.add
-	1 .A N... 000000 000000 100644 $_z40 $_z40 intent2.add
+	1 .A N... 000000 000000 100644 $ZERO_OID $ZERO_OID intent1.add
+	1 .A N... 000000 000000 100644 $ZERO_OID $ZERO_OID intent2.add
 	EOF

 	git status --porcelain=v2 >actual &&
@ -280,7 +280,7 @@ test_expect_success 'verify AA (add-add) conflict' '
 	cat >expect <<-EOF &&
 	# branch.oid $HM
 	# branch.head AA_M
-	u AA N... 000000 100644 100644 100644 $_z40 $OID_AA_B $OID_AA_A conflict.txt
+	u AA N... 000000 100644 100644 100644 $ZERO_OID $OID_AA_B $OID_AA_A conflict.txt
 	EOF

 	git status --porcelain=v2 --branch --untracked-files=all >actual &&
@ -373,7 +373,7 @@ test_expect_success 'verify upstream fields in branch header' '
 		## Test upstream-gone case. Fake this by pointing origin/master at
 		## a non-existing commit.
 		OLD=$(git rev-parse origin/master) &&
-		NEW=$_z40 &&
+		NEW=$ZERO_OID &&
 		mv .git/packed-refs .git/old-packed-refs &&
 		sed "s/$OLD/$NEW/g" <.git/old-packed-refs >.git/packed-refs &&

@ -469,8 +469,8 @@ test_expect_success 'create and add submodule, submodule appears clean (A. S...)
 		# branch.head master
 		# branch.upstream origin/master
 		# branch.ab +0 -0
-		1 A. N... 000000 100644 100644 $_z40 $HMOD .gitmodules
-		1 A. S... 000000 160000 160000 $_z40 $HSUB sub1
+		1 A. N... 000000 100644 100644 $ZERO_OID $HMOD .gitmodules
+		1 A. S... 000000 160000 160000 $ZERO_OID $HSUB sub1
 		EOF

 		git status --porcelain=v2 --branch --untracked-files=all >actual &&
@ -494,8 +494,8 @@ test_expect_success 'untracked changes in added submodule (AM S..U)' '
 		# branch.head master
 		# branch.upstream origin/master
 		# branch.ab +0 -0
-		1 A. N... 000000 100644 100644 $_z40 $HMOD .gitmodules
-		1 AM S..U 000000 160000 160000 $_z40 $HSUB sub1
+		1 A. N... 000000 100644 100644 $ZERO_OID $HMOD .gitmodules
+		1 AM S..U 000000 160000 160000 $ZERO_OID $HSUB sub1
 		EOF

 		git status --porcelain=v2 --branch --untracked-files=all >actual &&
@ -519,8 +519,8 @@ test_expect_success 'staged changes in added submodule (AM S.M.)' '
 		# branch.head master
 		# branch.upstream origin/master
 		# branch.ab +0 -0
-		1 A. N... 000000 100644 100644 $_z40 $HMOD .gitmodules
-		1 AM S.M. 000000 160000 160000 $_z40 $HSUB sub1
+		1 A. N... 000000 100644 100644 $ZERO_OID $HMOD .gitmodules
+		1 AM S.M. 000000 160000 160000 $ZERO_OID $HSUB sub1
 		EOF

 		git status --porcelain=v2 --branch --untracked-files=all >actual &&
@ -546,8 +546,8 @@ test_expect_success 'staged and unstaged changes in added (AM S.M.)' '
 		# branch.head master
 		# branch.upstream origin/master
 		# branch.ab +0 -0
-		1 A. N... 000000 100644 100644 $_z40 $HMOD .gitmodules
-		1 AM S.M. 000000 160000 160000 $_z40 $HSUB sub1
+		1 A. N... 000000 100644 100644 $ZERO_OID $HMOD .gitmodules
+		1 AM S.M. 000000 160000 160000 $ZERO_OID $HSUB sub1
 		EOF

 		git status --porcelain=v2 --branch --untracked-files=all >actual &&
@ -573,8 +573,8 @@ test_expect_success 'staged and untracked changes in added submodule (AM S.MU)'
 		# branch.head master
 		# branch.upstream origin/master
 		# branch.ab +0 -0
-		1 A. N... 000000 100644 100644 $_z40 $HMOD .gitmodules
-		1 AM S.MU 000000 160000 160000 $_z40 $HSUB sub1
+		1 A. N... 000000 100644 100644 $ZERO_OID $HMOD .gitmodules
+		1 AM S.MU 000000 160000 160000 $ZERO_OID $HSUB sub1
 		EOF

 		git status --porcelain=v2 --branch --untracked-files=all >actual &&
@ -600,8 +600,8 @@ test_expect_success 'commit within the submodule appears as new commit in super
 		# branch.head master
 		# branch.upstream origin/master
 		# branch.ab +0 -0
-		1 A. N... 000000 100644 100644 $_z40 $HMOD .gitmodules
-		1 AM SC.. 000000 160000 160000 $_z40 $HSUB sub1
+		1 A. N... 000000 100644 100644 $ZERO_OID $HMOD .gitmodules
+		1 AM SC.. 000000 160000 160000 $ZERO_OID $HSUB sub1
 		EOF

 		git status --porcelain=v2 --branch --untracked-files=all >actual &&
--- a/t/t7506-status-submodule.sh
+++ b/t/t7506-status-submodule.sh
@ -18,7 +18,7 @@ test_create_repo_with_commit () {
 }

 sanitize_output () {
-	sed -e "s/$_x40/HASH/" -e "s/$_x40/HASH/" output >output2 &&
+	sed -e "s/$OID_REGEX/HASH/" -e "s/$OID_REGEX/HASH/" output >output2 &&
 	mv output2 output
 }

--- a/t/t9010-svn-fe.sh
+++ b/t/t9010-svn-fe.sh
@ -473,7 +473,7 @@ test_expect_failure 'change file mode but keep old content' '
 	{
 		git rev-list HEAD |
 		git diff-tree --root --stdin |
-		sed "s/$_x40/OBJID/g"
+		sed "s/$OID_REGEX/OBJID/g"
 	} >actual &&
 	git show HEAD:greeting >actual.blob &&
 	git show HEAD^:greeting >actual.target &&
@ -573,7 +573,7 @@ test_expect_success 'NUL in log message, file content, and property name' '
 	{
 		git rev-list HEAD |
 		git diff-tree --root --stdin |
-		sed "s/$_x40/OBJID/g"
+		sed "s/$OID_REGEX/OBJID/g"
 	} >actual &&
 	{
 		git cat-file commit HEAD | nul_to_q &&
@ -659,7 +659,7 @@ test_expect_success 'change file mode and reiterate content' '
 	{
 		git rev-list HEAD |
 		git diff-tree --root --stdin |
-		sed "s/$_x40/OBJID/g"
+		sed "s/$OID_REGEX/OBJID/g"
 	} >actual &&
 	git show HEAD:greeting >actual.blob &&
 	git show HEAD^:greeting >actual.target &&
@ -792,7 +792,7 @@ test_expect_success 'property deltas supported' '
 	{
 		git rev-list HEAD |
 		git diff-tree --stdin |
-		sed "s/$_x40/OBJID/g"
+		sed "s/$OID_REGEX/OBJID/g"
 	} >actual &&
 	test_cmp expect actual
 '
@ -846,7 +846,7 @@ test_expect_success 'properties on /' '
 	{
 		git rev-list HEAD |
 		git diff-tree --root --always --stdin |
-		sed "s/$_x40/OBJID/g"
+		sed "s/$OID_REGEX/OBJID/g"
 	} >actual &&
 	test_cmp expect actual
 '
@ -931,7 +931,7 @@ test_expect_success 'deltas for typechange' '
 	{
 		git rev-list HEAD |
 		git diff-tree --root --stdin |
-		sed "s/$_x40/OBJID/g"
+		sed "s/$OID_REGEX/OBJID/g"
 	} >actual &&
 	test_cmp expect actual
 '
@ -1030,7 +1030,7 @@ test_expect_success 'deltas need not consume the whole preimage' '
 	{
 		git rev-list HEAD |
 		git diff-tree --root --stdin |
-		sed "s/$_x40/OBJID/g"
+		sed "s/$OID_REGEX/OBJID/g"
 	} >actual &&
 	test_cmp expect actual &&
 	git show HEAD:postimage >actual.3 &&
--- a/t/t9300-fast-import.sh
+++ b/t/t9300-fast-import.sh
@ -1185,7 +1185,7 @@ test_expect_success PIPE 'N: empty directory reads as missing' '
 	test_cmp expect.response response &&
 	git rev-list read-empty |
 	git diff-tree -r --root --stdin |
-	sed "s/$_x40/OBJNAME/g" >actual &&
+	sed "s/$OID_REGEX/OBJNAME/g" >actual &&
 	test_cmp expect actual
 '

@ -1271,7 +1271,7 @@ test_expect_success 'N: delete directory by copying' '
 	git fast-import <input &&
 	git rev-list N-delete |
 		git diff-tree -r --stdin --root --always |
-		sed -e "s/$_x40/OBJID/g" >actual &&
+		sed -e "s/$OID_REGEX/OBJID/g" >actual &&
 	test_cmp expect actual
 '

@ -2602,7 +2602,7 @@ test_expect_success 'R: terminating "done" within commit' '
 	EOF
 	git rev-list done-ends |
 	git diff-tree -r --stdin --root --always |
-	sed -e "s/$_x40/OBJID/g" >actual &&
+	sed -e "s/$OID_REGEX/OBJID/g" >actual &&
 	test_cmp expect actual
 '

--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@ -184,6 +184,8 @@ _x40="$_x35$_x05"
 # Zero SHA-1
 _z40=0000000000000000000000000000000000000000

+OID_REGEX="$_x40"
+ZERO_OID=$_z40
 EMPTY_TREE=4b825dc642cb6eb9a060e54bf8d69288fbee4904
 EMPTY_BLOB=e69de29bb2d1d6434b8b29ae775ad8c2e48c5391

@ -195,7 +197,7 @@ LF='
 # when case-folding filenames
 u200c=$(printf '\342\200\214')

-export _x05 _x35 _x40 _z40 LF u200c EMPTY_TREE EMPTY_BLOB
+export _x05 _x35 _x40 _z40 LF u200c EMPTY_TREE EMPTY_BLOB ZERO_OID OID_REGEX

 # Each test should start with something like this, after copyright notices:
 #
@ -1207,3 +1209,10 @@ test_lazy_prereq TIME_T_IS_64BIT 'test-tool date time_t-is64bit'
 test_lazy_prereq CURL '
 	curl --version
 '
+
+# SHA1 is a test if the hash algorithm in use is SHA-1.  This is both for tests
+# which will not work with other hash algorithms and tests that work but don't
+# test anything meaningful (e.g. special values which cause short collisions).
+test_lazy_prereq SHA1 '
+	test $(git hash-object /dev/null) = e69de29bb2d1d6434b8b29ae775ad8c2e48c5391
+'