Unit testing for def/ module.

Added unit tests to test code in def/ module.

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

@@ -14,3 +14,9 @@ func IsTerminal(fd uintptr) bool {
 	err := unix.IoctlSetTermio(int(fd), unix.TCGETA, &termio)
 	return err == nil
 }
+
+// IsCygwinTerminal return true if the file descriptor is a cygwin or msys2
+// terminal. This is also always false on this environment.
+func IsCygwinTerminal(fd uintptr) bool {
+	return false
+}