check-code: warning and fixes for whitespace in unified tests

contrib/check-code.py

@@ -74,6 +74,7 b' testfilters = ['
 uprefix = r"^  \$ "
 uprefixc = r"^  > "
 utestpats = [
+    (r'^(\S|  $ ).*(\S\s+|^\s+)\n', "trailing whitespace on non-output"),
     (uprefix + r'.*\|\s*sed', "use regex test output patterns instead of sed"),
     (uprefix + r'(true|exit 0)', "explicit zero exit unnecessary"),
     (uprefix + r'.*\$\?', "explicit exit code checks unnecessary"),