t1006: split test utility functions into new "lib-cat-file.sh"

This refactor extracts utility functions from the cat-file's test
script "t1006-cat-file.sh" into a new "lib-cat-file.sh" dedicated
library file. The goal is to improve code reuse and readability,
enabling future tests to leverage these utilities without duplicating
code.

Signed-off-by: Junio C Hamano <[email protected]>

Author: peijianju

t/lib-cat-file.sh

@@ -0,0 +1,16 @@
+# Library of git-cat-file related test functions.
+
+# Print a string without a trailing newline.
+echo_without_newline () {
+	printf '%s' "$*"
+}
+
+# Print a string without newlines and replace them with a NULL character (\0).
+echo_without_newline_nul () {
+	echo_without_newline "$@" | tr '\n' '\0'
+}
+
+# Calculate the length of a string.
+strlen () {
+	echo_without_newline "$1" | wc -c | sed -e 's/^ *//'
+}

t/t1006-cat-file.sh

@@ -3,6 +3,7 @@
 test_description='git cat-file'
 
 . ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-cat-file.sh
 
 test_cmdmode_usage () {
 	test_expect_code 129 "$@" 2>err &&
@@ -98,18 +99,6 @@ do
 	'
 done
 
-echo_without_newline () {
-    printf '%s' "$*"
-}
-
-echo_without_newline_nul () {
-	echo_without_newline "$@" | tr '\n' '\0'
-}
-
-strlen () {
-    echo_without_newline "$1" | wc -c | sed -e 's/^ *//'
-}
-
 run_tests () {
     type=$1
     oid=$2