[test] Add new CLI testing platform

Adds the new CLI testing platform that I'm proposing.
See the added `README.md` for details.

tests/cli-tests/common/permissions.sh

@@ -0,0 +1,18 @@
+source "$COMMON/platform.sh"
+
+GET_PERMS="stat -c %a"
+case "$UNAME" in
+    Darwin | FreeBSD | OpenBSD | NetBSD) GET_PERMS="stat -f %Lp" ;;
+esac
+
+assertFilePermissions() {
+    STAT1=$($GET_PERMS "$1")
+    STAT2=$2
+    [ "$STAT1" = "$STAT2" ] || die "permissions on $1 don't match expected ($STAT1 != $STAT2)"
+}
+
+assertSamePermissions() {
+    STAT1=$($GET_PERMS "$1")
+    STAT2=$($GET_PERMS "$2")
+    [ "$STAT1" = "$STAT2" ] || die "permissions on $1 don't match those on $2 ($STAT1 != $STAT2)"
+}