test-lib functions: add --printf option to test_commit

Add a --printf option to test_commit to allow writing to the file with
"printf" instead of "echo".

This is useful for writing "\n", "\0" etc., in particular in
combination with the --append option added in 3373518cc8 (test-lib
functions: add an --append option to test_commit, 2021-01-12).

I'm converting a few tests to use the new option rather than a manual
printf/add/commit combination to demonstrate its usefulness. While I'm
at it use "test_create_repo" where appropriate, and give the
first/second commit a meaningful/more conventional log message in
cases where no test cared about that message.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t1307-config-blob.sh

@@ -65,9 +65,7 @@ test_expect_success 'parse errors in blobs are properly attributed' '
 '
 
 test_expect_success 'can parse blob ending with CR' '
-	printf "[some]key = value\\r" >config &&
-	git add config &&
-	git commit -m CR &&
+	test_commit --printf CR config "[some]key = value\\r" &&
 	echo value >expect &&
 	git config --blob=HEAD:config some.key >actual &&
 	test_cmp expect actual

t/t2030-unresolve-info.sh

@@ -179,8 +179,7 @@ test_expect_success 'rerere and rerere forget (subdirectory)' '
 
 test_expect_success 'rerere forget (binary)' '
 	git checkout -f side &&
-	printf "a\0c" >binary &&
-	git commit -a -m binary &&
+	test_commit --printf binary binary "a\0c" &&
 	test_must_fail git merge second &&
 	git rerere forget binary
 '

t/t4006-diff-mode.sh

@@ -26,10 +26,8 @@ test_expect_success 'chmod' '
 '
 
 test_expect_success 'prepare binary file' '
-	git commit -m rezrov &&
-	printf "\00\01\02\03\04\05\06" >binbin &&
-	git add binbin &&
-	git commit -m binbin
+	git commit -m one &&
+	test_commit --printf two binbin "\00\01\02\03\04\05\06"
 '
 
 test_expect_success '--stat output after text chmod' '

t/t4030-diff-textconv.sh

@@ -26,12 +26,8 @@ EOF
 chmod +x hexdump
 
 test_expect_success 'setup binary file with history' '
-	printf "\\0\\n" >file &&
-	git add file &&
-	git commit -m one &&
-	printf "\\01\\n" >>file &&
-	git add file &&
-	git commit -m two
+	test_commit --printf one file "\\0\\n" &&
+	test_commit --printf --append two file "\\01\\n"
 '
 
 test_expect_success 'file is considered binary by porcelain' '

t/t5520-pull.sh

@@ -746,14 +746,8 @@ test_expect_success 'pull --rebase fails on corrupt HEAD' '
 '
 
 test_expect_success 'setup for detecting upstreamed changes' '
-	mkdir src &&
-	(
-		cd src &&
-		git init &&
-		printf "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n" > stuff &&
-		git add stuff &&
-		git commit -m "Initial revision"
-	) &&
+	test_create_repo src &&
+	test_commit -C src --printf one stuff "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n" &&
 	git clone src dst &&
 	(
 		cd src &&

t/test-lib-functions.sh

@@ -173,6 +173,12 @@ debug () {
 #	Do not call test_tick before making a commit
 #   --append
 #	Use ">>" instead of ">" when writing "<contents>" to "<file>"
+#   --printf
+#       Use "printf" instead of "echo" when writing "<contents>" to
+#       "<file>", use this to write escape sequences such as "\0", a
+#       trailing "\n" won't be added automatically. This option
+#       supports nothing but the FORMAT of printf(1), i.e. no custom
+#       ARGUMENT(s).
 #   --signoff
 #	Invoke "git commit" with --signoff
 #   --author <author>
@@ -191,6 +197,7 @@ debug () {
 
 test_commit () {
 	notick= &&
+	echo=echo &&
 	append= &&
 	author= &&
 	signoff= &&
@@ -202,6 +209,9 @@ test_commit () {
 		--notick)
 			notick=yes
 			;;
+		--printf)
+			echo=printf
+			;;
 		--append)
 			append=yes
 			;;
@@ -238,9 +248,9 @@ test_commit () {
 	file=${2:-"$1.t"} &&
 	if test -n "$append"
 	then
-		echo "${3-$1}" >>"$indir$file"
+		$echo "${3-$1}" >>"$indir$file"
 	else
-		echo "${3-$1}" >"$indir$file"
+		$echo "${3-$1}" >"$indir$file"
 	fi &&
 	git ${indir:+ -C "$indir"} add "$file" &&
 	if test -z "$notick"