Unit testing for def/ module.

Added unit tests to test code in def/ module.

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

@@ -0,0 +1,19 @@
+// +build linux aix
+// +build !appengine
+// +build !android
+
+package isatty
+
+import "golang.org/x/sys/unix"
+
+// IsTerminal return true if the file descriptor is terminal.
+func IsTerminal(fd uintptr) bool {
+	_, err := unix.IoctlGetTermios(int(fd), unix.TCGETS)
+	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
+}