diff --git a/tests/Makefile.am b/tests/Makefile.am
index fdc1639..bd3e330 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -42,6 +42,7 @@ TESTS = \
 	git-cleanup \
 	garbage \
 	global-reject-files \
+	hardlinks \
 	inname \
 	line-numbers \
 	merge \
diff --git a/tests/file-create-modes b/tests/file-create-modes
index 2ea44ec..e80a79a 100644
--- a/tests/file-create-modes
+++ b/tests/file-create-modes
@@ -10,6 +10,7 @@
 
 require cat
 require sed
+require chmod
 use_local_patch
 use_tmpdir
 
diff --git a/tests/file-modes b/tests/file-modes
index 8475182..9c28dd8 100644
--- a/tests/file-modes
+++ b/tests/file-modes
@@ -10,6 +10,7 @@
 
 require cat
 require sed
+require chmod
 use_local_patch
 use_tmpdir
 
diff --git a/tests/hardlinks b/tests/hardlinks
new file mode 100644
index 0000000..7eb3a28
--- /dev/null
+++ b/tests/hardlinks
@@ -0,0 +1,50 @@
+# Copyright 2009-2024 Free Software Foundation, Inc.
+#
+# Copying and distribution of this file, with or without modification,
+# in any medium, are permitted without royalty provided the copyright
+# notice and this notice are preserved.
+
+# Patch must not overwrite backup files it has created itself.
+# (Backup file tests for symlinks are in tests/symlinks.)
+
+. $srcdir/test-lib.sh
+
+require cat
+require hardlinks
+use_local_patch
+use_tmpdir
+
+# ==============================================================
+
+# Hardlinks between source files
+
+echo one > f
+ln f g
+
+cat > fg.diff <<EOF
+--- f.orig
++++ f
+@@ -2 +2 @@
+-one
++two
+--- g.orig
++++ g
+@@ -2 +2 @@
+-one
++two
+EOF
+
+check 'patch -p0 < fg.diff' <<EOF
+patching file f
+Hunk #1 succeeded at 1 (offset -1 lines).
+patching file g
+Hunk #1 succeeded at 1 (offset -1 lines).
+EOF
+
+check 'cat f.orig' <<EOF
+one
+EOF
+
+check 'cat g.orig' <<EOF
+one
+EOF
diff --git a/tests/no-mode-change-git-diff b/tests/no-mode-change-git-diff
index 50497e0..eaf860b 100644
--- a/tests/no-mode-change-git-diff
+++ b/tests/no-mode-change-git-diff
@@ -9,6 +9,7 @@
 require cat
 require chmod
 require stat
+require chmod
 use_local_patch
 use_tmpdir
 
diff --git a/tests/preserve-mode-and-timestamp b/tests/preserve-mode-and-timestamp
index 07d4370..7e8ff84 100644
--- a/tests/preserve-mode-and-timestamp
+++ b/tests/preserve-mode-and-timestamp
@@ -8,6 +8,7 @@
 
 require cat
 require sed
+require chmod
 use_local_patch
 use_tmpdir
 
diff --git a/tests/quoted-filenames b/tests/quoted-filenames
index ec1d376..54982da 100644
--- a/tests/quoted-filenames
+++ b/tests/quoted-filenames
@@ -9,13 +9,15 @@
 . $srcdir/test-lib.sh
 
 require cat
+require special_characters
 use_local_patch
 use_tmpdir
 
 # ==============================================================
 
 # Forbidden characters in Windows filenames:
-#   \ / : * ? " < > |
+#   \ / : * ? " < > | TAB
+# Filenames with trailing space characters
 
 cat > d.diff <<EOF
 --- "\\t \\040"
diff --git a/tests/read-only-files b/tests/read-only-files
index f188a3d..b28b93d 100644
--- a/tests/read-only-files
+++ b/tests/read-only-files
@@ -9,6 +9,7 @@
 . $srcdir/test-lib.sh
 
 require cat
+require chmod
 use_local_patch
 use_tmpdir
 
diff --git a/tests/remember-backup-files b/tests/remember-backup-files
index 13406fa..e8d7f25 100644
--- a/tests/remember-backup-files
+++ b/tests/remember-backup-files
@@ -50,41 +50,6 @@ EOF
 
 # ==============================================================
 
-# Hardlinks between source files
-
-echo one > f
-ln f g
-
-cat > fg.diff <<EOF
---- f.orig
-+++ f
-@@ -2 +2 @@
--one
-+two
---- g.orig
-+++ g
-@@ -2 +2 @@
--one
-+two
-EOF
-
-check 'patch -p0 < fg.diff' <<EOF
-patching file f
-Hunk #1 succeeded at 1 (offset -1 lines).
-patching file g
-Hunk #1 succeeded at 1 (offset -1 lines).
-EOF
-
-check 'cat f.orig' <<EOF
-one
-EOF
-
-check 'cat g.orig' <<EOF
-one
-EOF
-
-# ==============================================================
-
 echo one > f
 
 cat > f.diff <<EOF
diff --git a/tests/symlinks b/tests/symlinks
index aff283a..daca8a3 100644
--- a/tests/symlinks
+++ b/tests/symlinks
@@ -9,6 +9,7 @@
 . $srcdir/test-lib.sh
 
 require cat
+require symlinks
 use_local_patch
 use_tmpdir
 
diff --git a/tests/test-lib.sh b/tests/test-lib.sh
index 7fb1363..ba755dc 100644
--- a/tests/test-lib.sh
+++ b/tests/test-lib.sh
@@ -7,7 +7,7 @@
 
 # FIXME: Requires a version of diff that understands "-u".
 
-require_gnu_diff() {
+_require_gnu_diff() {
     case "`diff --version 2> /dev/null`" in
     *GNU*)
 	;;
@@ -17,10 +17,55 @@ require_gnu_diff() {
     esac
 }
 
+_try_chmod() {
+    chmod "$1" "$2" && test "`ls -l "$2" | cut -b2-10`" = "$3"
+}
+
+_require_chmod() {
+    tmp=`mktemp working-chmod.XXXXXXXX`
+    if ! _try_chmod 644 "$tmp" "rw-r--r--" || \
+       ! _try_chmod 600 "$tmp" "rw-------"; then
+	rm -f "$tmp"
+	echo "This test requires chmod support" >&2
+	exit 77
+    fi
+    rm -f "$tmp"
+}
+
+_require_hardlinks() {
+    tmpdir=`mktemp -d hardlinks.XXXXXXXX`
+    if ! touch "$tmpdir/f" ||
+       ! ln "$tmpdir/f" "$tmpdir/g"; then
+	rm -rf "$tmpdir"
+	echo "This test requires hardlink support" >&2
+	exit 77
+    fi
+    rm -rf "$tmpdir"
+}
+
+_require_symlinks() {
+    tmpdir=`mktemp -d hardlinks.XXXXXXXX`
+    if ! touch "$tmpdir/f" ||
+       ! ln -s "f" "$tmpdir/g"; then
+	rm -rf "$tmpdir"
+	echo "This test requires symlink support" >&2
+	exit 77
+    fi
+    rm -rf "$tmpdir"
+}
+
+_require_special_characters() {
+    if ! tmp=`mktemp '	 '.XXXXXXXX`; then
+	echo "This test requires special character support in filenames" >&2
+	exit 77
+    fi
+    rm -f "$tmp"
+}
+
 require() {
     utility="$1"
-    if type require_${utility} > /dev/null 2> /dev/null; then
-	require_${utility}
+    if type _require_${utility} > /dev/null 2> /dev/null; then
+	_require_${utility}
     elif ! type "${utility}" > /dev/null 2> /dev/null; then
 	echo "This test requires the ${utility} utility" >&2
 	exit 77
diff --git a/tests/unmodified-files b/tests/unmodified-files
index 93d078a..77cb8bc 100644
--- a/tests/unmodified-files
+++ b/tests/unmodified-files
@@ -7,6 +7,7 @@
 . $srcdir/test-lib.sh
 
 require cat
+require hardlinks
 use_local_patch
 use_tmpdir