test-lib.sh: introduce and use $EMPTY_TREE

This is a special SHA1. Let's keep it at one place, easier to replace
later when the hash change comes, easier to recognize.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t0000-basic.sh

@@ -834,7 +834,7 @@ test_expect_success 'git write-tree should be able to write an empty tree' '
 '
 
 test_expect_success 'validate object ID of a known tree' '
-	test "$tree" = 4b825dc642cb6eb9a060e54bf8d69288fbee4904
+	test "$tree" = $EMPTY_TREE
 '
 
 # Various types of objects

t/t1100-commit-tree-options.sh

@@ -15,7 +15,7 @@ Also make sure that command line parser understands the normal
 . ./test-lib.sh
 
 cat >expected <<EOF
-tree 4b825dc642cb6eb9a060e54bf8d69288fbee4904
+tree $EMPTY_TREE
 author Author Name <author@email> 1117148400 +0000
 committer Committer Name <committer@email> 1117150200 +0000
 

t/t4010-diff-pathspec.sh

@@ -78,8 +78,6 @@ test_expect_success 'diff-tree pathspec' '
 	test_cmp expected current
 '
 
-EMPTY_TREE=4b825dc642cb6eb9a060e54bf8d69288fbee4904
-
 test_expect_success 'diff-tree with wildcard shows dir also matches' '
 	git diff-tree --name-only $EMPTY_TREE $tree -- "f*" >result &&
 	echo file0 >expected &&

t/t4054-diff-bogus-tree.sh

@@ -3,8 +3,6 @@
 test_description='test diff with a bogus tree containing the null sha1'
 . ./test-lib.sh
 
-empty_tree=4b825dc642cb6eb9a060e54bf8d69288fbee4904
-
 test_expect_success 'create bogus tree' '
 	bogus_tree=$(
 		printf "100644 fooQQQQQQQQQQQQQQQQQQQQQ" |
@@ -22,13 +20,13 @@ 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 &&
-	git diff-tree $empty_tree $bogus_tree >actual &&
+	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 &&
-	git diff-tree $bogus_tree $empty_tree >actual &&
+	git diff-tree $bogus_tree $EMPTY_TREE >actual &&
 	test_cmp expect actual
 '
 
@@ -57,11 +55,11 @@ test_expect_success 'raw diff shows null sha1 (index)' '
 '
 
 test_expect_success 'patch fails due to bogus sha1 (addition)' '
-	test_must_fail git diff-tree -p $empty_tree $bogus_tree
+	test_must_fail git diff-tree -p $EMPTY_TREE $bogus_tree
 '
 
 test_expect_success 'patch fails due to bogus sha1 (removal)' '
-	test_must_fail git diff-tree -p $bogus_tree $empty_tree
+	test_must_fail git diff-tree -p $bogus_tree $EMPTY_TREE
 '
 
 test_expect_success 'patch fails due to bogus sha1 (modification)' '

t/t5504-fetch-receive-strict.sh

@@ -115,8 +115,8 @@ test_expect_success 'push with transfer.fsckobjects' '
 	test_cmp exp act
 '
 
-cat >bogus-commit <<\EOF
-tree 4b825dc642cb6eb9a060e54bf8d69288fbee4904
+cat >bogus-commit <<EOF
+tree $EMPTY_TREE
 author Bugs Bunny 1234567890 +0000
 committer Bugs Bunny <bugs@bun.ni> 1234567890 +0000
 

t/test-lib.sh

@@ -162,6 +162,8 @@ _x40="$_x05$_x05$_x05$_x05$_x05$_x05$_x05$_x05"
 # Zero SHA-1
 _z40=0000000000000000000000000000000000000000
 
+EMPTY_TREE=4b825dc642cb6eb9a060e54bf8d69288fbee4904
+
 # Line feed
 LF='
 '
@@ -170,7 +172,7 @@ LF='
 # when case-folding filenames
 u200c=$(printf '\342\200\214')
 
-export _x05 _x40 _z40 LF u200c
+export _x05 _x40 _z40 LF u200c EMPTY_TREE
 
 # Each test should start with something like this, after copyright notices:
 #