Add unit test for RTRIM-bug

Author: Joe7M

samples/distro-examples/tests/strings.bas

@@ -209,4 +209,9 @@ for t in number_test
   if (t[1] != bin(t[0])) then throw "err: bin(" + str(t[0]) + ") <> " + t[1]
   if (t[2] != oct(t[0])) then throw "err: oct(" + str(t[0]) + ") <> " + t[2]
   if (t[3] != hex(t[0])) then throw "err: hex(" + str(t[0]) + ") <> " + t[3]
-next
+next
+
+REM Bug: RTRIM trimed input string on the right side
+s1 = "   test   "
+s2 = rtrim(s1)
+if(s1 != "   test   ") then throw "err: RTRIM changed input string"