specify posix.ctype:

- before:

    ctype = require "posix.ctype"

- describe isgraph:

  - before:

      isgraph = ctype.isgraph

  - context with bad arguments:

      badargs.diagnose (isgraph, "(string)")

  - it returns non-zero for successful tests:

      expect (type (isgraph 'a')).to_be "number"

      expect (isgraph 'a').not_to_be (0)

  - it returns zero for failed tests:

      expect (isgraph ' ').to_be (0)

- describe isprint:

  - before:

      isprint = ctype.isprint

  - context with bad arguments:

      badargs.diagnose (isprint, "(string)")

  - it returns non-zero for successful tests:

      expect (type (isprint 'a')).to_be "number"

      expect (isprint 'a').not_to_be (0)

  - it returns zero for failed tests:

      expect (isprint (string.char (0))).to_be (0)