Added more tests

tty/Terminal_darwin.go

@@ -1,6 +1,9 @@
 package tty
 
+import "golang.org/x/sys/unix"
+
 // IsTerminal returns true if the file descriptor is a terminal.
 func IsTerminal(fd uintptr) bool {
-	return false
+	_, err := unix.IoctlGetTermios(int(fd), unix.TIOCGETA)
+	return err == nil
 }

tty/Terminal_test.go

@@ -0,0 +1,12 @@
+package tty_test
+
+import (
+	"os"
+	"testing"
+
+	"git.akyoto.dev/go/color/tty"
+)
+
+func TestIsTerminal(t *testing.T) {
+	tty.IsTerminal(os.Stdout.Fd())
+}