diff --git a/xbee/session.go b/xbee/session.go
index f6d6b78..fcea905 100644
--- a/xbee/session.go
+++ b/xbee/session.go
@@ -177,18 +177,17 @@ func (sess *Session) writeAddr(p []byte, dest uint64) (n int, err error) {
 	if err != nil {
 		return
 	}
-	n = n - 4
+	n = len(p)
 
 	// finally, wait for the channel we got to return. this means that
 	// the matching response frame was received, so we can parse it.
-	// TODO: add timeout.
 
 	var status *TxStatusFrame
 	select {
 	case responseFrame := <-ch:
 		status, err = ParseTxStatusFrame(responseFrame)
 	case <-time.After(1 * time.Second):
-		return n, errors.New("timeout waiting for response")
+		return 0, errors.New("timeout waiting for response")
 	}
 
 
@@ -321,7 +320,7 @@ func (c *Conn) Read(p []byte) (n int, err error) {
 
 func (c *Conn) Close() error {
 	// remove ourselves from the conn list.
-
+	delete(c.parent.conns, uint64(c.addr))
 	return nil
 }
 
@@ -378,7 +377,9 @@ func ParseDeviceString(dev string) (*Transport, error) {
 
 		addr, _ := strings.CutPrefix(dev, "tcp://")
 
+		// FIXME: use default port (9750) if port not provided.
 		conn, err := net.Dial("tcp", addr)
+
 		if err != nil {
 			return nil, err
 		}
diff --git a/xbee/session_test.go b/xbee/session_test.go
index 85f7b19..176fbde 100644
--- a/xbee/session_test.go
+++ b/xbee/session_test.go
@@ -10,12 +10,12 @@ package xbee
 import (
 	"encoding/binary"
 	"os"
+	"reflect"
 	"testing"
 
 	"golang.org/x/exp/slog"
 )
 
-
 func TestXBeeHardware(t *testing.T) {
 	// this test runs only if the environemnt variable
 	// XBEE_DEVICE is set.
@@ -27,7 +27,6 @@ func TestXBeeHardware(t *testing.T) {
 	}
 
 	var sess *Session = nil
-	defer sess.Close()
 	// test connection.
 	t.Run("Connect to device", func(t *testing.T) {
 		dev, err := ParseDeviceString(devStr)
@@ -44,11 +43,11 @@ func TestXBeeHardware(t *testing.T) {
 		// }
 
 	})
-	
+
 	// now we should test sending a packet. and getting a response.
 
 	t.Run("Get Network ID", func(t *testing.T) {
-		b, err := sess.ATCommand([2]rune{'I','D'}, nil, false)
+		b, err := sess.ATCommand([2]rune{'I', 'D'}, nil, false)
 		if err != nil {
 			t.Errorf("ATCommand() error = %v", err)
 		}
@@ -58,17 +57,50 @@ func TestXBeeHardware(t *testing.T) {
 	})
 
 	t.Run("Check NP", func(t *testing.T) {
-		b, err := sess.ATCommand([2]rune{'N','P'}, nil, false)
+		b, err := sess.ATCommand([2]rune{'N', 'P'}, nil, false)
 
 		if err != nil {
 			t.Errorf("ATCommand() error = %v", err)
 		}
 
 		val := binary.BigEndian.Uint16(b)
-		if val != 0x100 {
-			t.Errorf("NP response wrong, expected 0x100 got %x", val)
+		if val != 0x100 && val != 0x640 {
+			t.Errorf("NP response wrong, expected 0x100 or 0x640 got 0x%X", val)
 		}
 	})
 
-
+}
+
+func TestParseDeviceString(t *testing.T) {
+	type args struct {
+		dev string
+	}
+	tests := []struct {
+		name    string
+		args    args
+		want    *Transport
+		wantErr bool
+	}{
+		{
+			name: "invalid stuff",
+			args: args{
+				dev: "blah",
+			},
+			want: nil,
+			wantErr: true,
+		},
+		// TODO: moar tests!
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ParseDeviceString(tt.args.dev)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("ParseDeviceString() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("ParseDeviceString() = %v, want %v", got, tt.want)
+			}
+		})
+	}
 }