Added more testcases

protocols/bgp/server/update_helper_test.go

 package server
 
 import (
+	"io"
 	"testing"
 
 	"bytes"
 
 	"github.com/bio-routing/bio-rd/protocols/bgp/packet"
 
+	"errors"
+
 	"github.com/bio-routing/bio-rd/net"
 	"github.com/stretchr/testify/assert"
 )
 
+type failingUpdate struct{}
+
+func (f *failingUpdate) SerializeUpdate() ([]byte, error) {
+	return nil, errors.New("general error")
+}
+
+type WriterByter interface {
+	Bytes() []byte
+	io.Writer
+}
+
+type failingReadWriter struct {
+}
+
+func (f *failingReadWriter) Write(p []byte) (n int, err error) {
+	return 0, errors.New("general error")
+}
+
+func (f *failingReadWriter) Bytes() []byte {
+	return []byte{}
+}
+
 func TestSerializeAndSendUpdate(t *testing.T) {
 	tests := []struct {
 		name       string
+		buf        WriterByter
 		err        error
 		testUpdate serializeAbleUpdate
 		expected   []byte
 	}{
 		{
 			name: "normal bgp update",
+			buf:  bytes.NewBuffer(nil),
 			err:  nil,
 			testUpdate: &packet.BGPUpdate{
 				WithdrawnRoutesLen: 5,
@@ -40,14 +67,37 @@ func TestSerializeAndSendUpdate(t *testing.T) {
 				0, 5, 8, 10, 16, 192, 168, 0, 0, // 2 withdraws
 			},
 		},
+		{
+			name:       "failed serialization",
+			buf:        bytes.NewBuffer(nil),
+			err:        nil,
+			testUpdate: &failingUpdate{},
+			expected:   nil,
+		},
+		{
+			name: "failed connection",
+			buf:  &failingReadWriter{},
+			err:  errors.New("Failed sending Update: general error"),
+			testUpdate: &packet.BGPUpdate{
+				WithdrawnRoutesLen: 5,
+				WithdrawnRoutes: &packet.NLRI{
+					IP:     strAddr("10.0.0.0"),
+					Pfxlen: 8,
+					Next: &packet.NLRI{
+						IP:     strAddr("192.168.0.0"),
+						Pfxlen: 16,
+					},
+				},
+			},
+			expected: []byte{},
+		},
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			buf := bytes.NewBuffer(nil)
-			err := serializeAndSendUpdate(buf, test.testUpdate)
+			err := serializeAndSendUpdate(test.buf, test.testUpdate)
 			assert.Equal(t, test.err, err)
 
-			assert.Equal(t, test.expected, buf.Bytes())
+			assert.Equal(t, test.expected, test.buf.Bytes())
 		})
 
 	}