describe lposix:

- before:

    fcntl, fileno = posix.fcntl, posix.fileno

    O_NONBLOCK = posix.O_NONBLOCK

- context with fcntl F_GETFL:

  - before:

      F_GETFL, F_SETFL = posix.F_GETFL, posix.F_SETFL

      fdin  = fileno (io.stdin)

      flags = fcntl (fdin, F_GETFL)

      restore = flags

  - after:

      fcntl (fdin, F_SETFL, restore)

  - it returns flags as a non-negative number:

      expect (type (flags)).should_be "number"

      expect (flags >= 0).should_be (true)

  - it resets O_NONBLOCK bit, if any:

      fcntl (fdin, F_SETFL, band (flags, bnot (O_NONBLOCK)))

      flags = fcntl (fdin, F_GETFL)

      expect (band (flags, O_NONBLOCK)).should_be (0)

  - it sets O_NONBLOCK bit:

      fcntl (fdin, F_SETFL, bor (flags, O_NONBLOCK))

      flags = fcntl (fdin, F_GETFL)

      expect (band (flags, O_NONBLOCK)).should_not_be (0)

  - it returns nil for negative fd argument:

      ret, msg, errno = fcntl (-7, F_GETFL)

      expect (ret).should_be (nil)

  - it returns nil for unopened fd argument:

      ret, msg, errno = fcntl (666, F_GETFL)

      expect (ret).should_be (nil)

  - it diagnoses incorrect userdata argument:

      expect (fcntl ("foobar", F_GETFL)).should_error "int expected"