Unit testing for def/ module.

Added unit tests to test code in def/ module.

vendor/github.com/mattn/go-isatty/isatty_linux.go

@@ -1,18 +0,0 @@
-// +build linux
-// +build !appengine,!ppc64,!ppc64le
-
-package isatty
-
-import (
-	"syscall"
-	"unsafe"
-)
-
-const ioctlReadTermios = syscall.TCGETS
-
-// IsTerminal return true if the file descriptor is terminal.
-func IsTerminal(fd uintptr) bool {
-	var termios syscall.Termios
-	_, _, err := syscall.Syscall6(syscall.SYS_IOCTL, fd, ioctlReadTermios, uintptr(unsafe.Pointer(&termios)), 0, 0, 0)
-	return err == 0
-}