diff --git a/device/device_test.go b/device/device_test.go
index db5a3c0..b6212b5 100644
--- a/device/device_test.go
+++ b/device/device_test.go
@@ -9,21 +9,17 @@ package device
  * without network dependencies
  */
 
-import "testing"
+import (
+	"bytes"
+	"testing"
+)
 
 func TestDevice(t *testing.T) {
 
 	// prepare tun devices for generating traffic
 
-	tun1, err := CreateDummyTUN("tun1")
-	if err != nil {
-		t.Error("failed to create tun:", err.Error())
-	}
-
-	tun2, err := CreateDummyTUN("tun2")
-	if err != nil {
-		t.Error("failed to create tun:", err.Error())
-	}
+	tun1 := newDummyTUN("tun1")
+	tun2 := newDummyTUN("tun2")
 
 	_ = tun1
 	_ = tun2
@@ -46,3 +42,27 @@ func TestDevice(t *testing.T) {
 	// create binds
 
 }
+
+func randDevice(t *testing.T) *Device {
+	sk, err := newPrivateKey()
+	if err != nil {
+		t.Fatal(err)
+	}
+	tun := newDummyTUN("dummy")
+	logger := NewLogger(LogLevelError, "")
+	device := NewDevice(tun, logger)
+	device.SetPrivateKey(sk)
+	return device
+}
+
+func assertNil(t *testing.T, err error) {
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func assertEqual(t *testing.T, a []byte, b []byte) {
+	if bytes.Compare(a, b) != 0 {
+		t.Fatal(a, "!=", b)
+	}
+}
diff --git a/device/tun_test.go b/device/tun_test.go
new file mode 100644
index 0000000..fbe4c1d
--- /dev/null
+++ b/device/tun_test.go
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2017-2019 WireGuard LLC. All Rights Reserved.
+ */
+
+package device
+
+import (
+	"errors"
+	"os"
+
+	"golang.zx2c4.com/wireguard/tun"
+)
+
+// newDummyTUN creates a dummy TUN device with the specified name.
+func newDummyTUN(name string) tun.TUNDevice {
+	return &dummyTUN{
+		name:    name,
+		packets: make(chan []byte, 100),
+		events:  make(chan tun.TUNEvent, 10),
+	}
+}
+
+// A dummyTUN is a tun.TUNDevice which is used in unit tests.
+type dummyTUN struct {
+	name    string
+	mtu     int
+	packets chan []byte
+	events  chan tun.TUNEvent
+}
+
+func (d *dummyTUN) Events() chan tun.TUNEvent { return d.events }
+func (*dummyTUN) File() *os.File              { return nil }
+func (*dummyTUN) Flush() error                { return nil }
+func (d *dummyTUN) MTU() (int, error)         { return d.mtu, nil }
+func (d *dummyTUN) Name() (string, error)     { return d.name, nil }
+
+func (d *dummyTUN) Close() error {
+	close(d.events)
+	close(d.packets)
+	return nil
+}
+
+func (d *dummyTUN) Read(b []byte, offset int) (int, error) {
+	buf, ok := <-d.packets
+	if !ok {
+		return 0, errors.New("device closed")
+	}
+	copy(b[offset:], buf)
+	return len(buf), nil
+}
+
+func (d *dummyTUN) Write(b []byte, offset int) (int, error) {
+	d.packets <- b[offset:]
+	return len(b), nil
+}
diff --git a/tun/helper_test.go b/tun/helper_test.go
deleted file mode 100644
index 4fa0357..0000000
--- a/tun/helper_test.go
+++ /dev/null
@@ -1,93 +0,0 @@
-/* SPDX-License-Identifier: MIT
- *
- * Copyright (C) 2017-2019 WireGuard LLC. All Rights Reserved.
- */
-
-package tun
-
-import (
-	"bytes"
-	"errors"
-	"os"
-	"testing"
-
-	"golang.zx2c4.com/wireguard/tun"
-)
-
-/* Helpers for writing unit tests
- */
-
-type DummyTUN struct {
-	name    string
-	mtu     int
-	packets chan []byte
-	events  chan tun.TUNEvent
-}
-
-func (tun *DummyTUN) File() *os.File {
-	return nil
-}
-
-func (tun *DummyTUN) Name() (string, error) {
-	return tun.name, nil
-}
-
-func (tun *DummyTUN) MTU() (int, error) {
-	return tun.mtu, nil
-}
-
-func (tun *DummyTUN) Write(d []byte, offset int) (int, error) {
-	tun.packets <- d[offset:]
-	return len(d), nil
-}
-
-func (tun *DummyTUN) Close() error {
-	close(tun.events)
-	close(tun.packets)
-	return nil
-}
-
-func (tun *DummyTUN) Events() chan tun.TUNEvent {
-	return tun.events
-}
-
-func (tun *DummyTUN) Read(d []byte, offset int) (int, error) {
-	t, ok := <-tun.packets
-	if !ok {
-		return 0, errors.New("device closed")
-	}
-	copy(d[offset:], t)
-	return len(t), nil
-}
-
-func CreateDummyTUN(name string) (tun.TUNDevice, error) {
-	var dummy DummyTUN
-	dummy.mtu = 0
-	dummy.packets = make(chan []byte, 100)
-	dummy.events = make(chan tun.TUNEvent, 10)
-	return &dummy, nil
-}
-
-func assertNil(t *testing.T, err error) {
-	if err != nil {
-		t.Fatal(err)
-	}
-}
-
-func assertEqual(t *testing.T, a []byte, b []byte) {
-	if bytes.Compare(a, b) != 0 {
-		t.Fatal(a, "!=", b)
-	}
-}
-
-func randDevice(t *testing.T) *Device {
-	sk, err := newPrivateKey()
-	if err != nil {
-		t.Fatal(err)
-	}
-	tun, _ := CreateDummyTUN("dummy")
-	logger := NewLogger(LogLevelError, "")
-	device := NewDevice(tun, logger)
-	device.SetPrivateKey(sk)
-	return device
-}