add error-flow unit test

Signed-off-by: Guy Daich <guy.daich@sap.com>

internal/utils/protocov/protocov.go

@@ -6,6 +6,7 @@
 package protocov
 
 import (
+	"errors"
 	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/types/known/anypb"
 )
@@ -19,6 +20,9 @@ var (
 )
 
 func ToAnyWithError(msg proto.Message) (*anypb.Any, error) {
+	if msg == nil {
+		return nil, errors.New("empty message received")
+	}
 	b, err := marshalOpts.Marshal(msg)
 	if err != nil {
 		return nil, err

internal/xds/translator/listener_test.go

@@ -0,0 +1,44 @@
+// Copyright Envoy Gateway Authors
+// SPDX-License-Identifier: Apache-2.0
+// The full text of the Apache license is available in the LICENSE file at
+// the root of the repo.
+
+package translator
+
+import (
+	"errors"
+	"testing"
+
+	hcmv3 "github.com/envoyproxy/go-control-plane/envoy/extensions/filters/network/http_connection_manager/v3"
+	"github.com/stretchr/testify/assert"
+	"google.golang.org/protobuf/proto"
+)
+
+func Test_toNetworkFilter(t *testing.T) {
+	tests := []struct {
+		name    string
+		proto   proto.Message
+		wantErr error
+	}{
+		{
+			name:    "valid filter",
+			proto:   &hcmv3.HttpConnectionManager{},
+			wantErr: nil,
+		},
+		{
+			name:    "invalid proto msg",
+			proto:   nil,
+			wantErr: errors.New("empty message received"),
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := toNetworkFilter("name", tt.proto)
+			if tt.wantErr != nil {
+				assert.Equalf(t, tt.wantErr, err, "toNetworkFilter(%v)", tt.proto)
+			} else {
+				assert.Equalf(t, nil, err, "toNetworkFilter(%v)", tt.proto)
+			}
+		})
+	}
+}