test is not posix

[Trek <trek00@inbox.ru>]

the -n and -z options of the test utility are not posixly correct if the
argument is "!", "(", ")" or "-a"

with a posix shell:

  $ sh -c 'test -n "!" && echo ok'
  ok

with zsh called as sh:

  $ zsh/sh -c 'test -n "!" && echo ok'
  zsh:test:1: too many arguments

a workaround exist:

  $ zsh/sh -c 'test "X!" != "X" && echo ok'
  ok

but the posix standard requires -n and -z to be safe even if the
argument is '!' or '(':

  The two commands: test "$1" and test ! "$1" could not be used reliably
  on some historical systems. Unexpected results would occur if such a
  string expression were used and $1 expanded to '!', '(', or a known
  unary primary. Better constructs are: test -n "$1" and test -z "$1"
  respectively. 

http://pubs.opengroup.org/onlinepubs/9699919799/utilities/test.html#tag_20_128_16


I discovered this bug developing a small shell library, where you can
find an use case in the n_str_set function of the lib/str.sh file
included in http://www.trek.eu.org/devel/naive/naive-0.0.2.tar.gz

c-ya!