Don't add TCP proxy when error occurs during creation.

pkg/server/service/tcp/service_test.go

@@ -0,0 +1,82 @@
+package tcp
+
+import (
+	"context"
+	"testing"
+
+	"github.com/containous/traefik/pkg/config"
+	"github.com/stretchr/testify/require"
+)
+
+func TestManager_BuildTCP(t *testing.T) {
+	testCases := []struct {
+		desc          string
+		serviceName   string
+		configs       map[string]*config.TCPService
+		expectedError string
+	}{
+		{
+			desc:          "without configuration",
+			serviceName:   "test",
+			configs:       nil,
+			expectedError: `the service "test" does not exits`,
+		},
+		{
+			desc:        "missing lb configuration",
+			serviceName: "test",
+			configs: map[string]*config.TCPService{
+				"test": {},
+			},
+			expectedError: `the service "test" doesn't have any TCP load balancer`,
+		},
+		{
+			desc:        "no such host",
+			serviceName: "test",
+			configs: map[string]*config.TCPService{
+				"test": {
+					LoadBalancer: &config.TCPLoadBalancerService{
+						Servers: []config.TCPServer{
+							{Address: "test:31"},
+						},
+					},
+				},
+			},
+		},
+		{
+			desc:        "invalid IP address",
+			serviceName: "test",
+			configs: map[string]*config.TCPService{
+				"test": {
+					LoadBalancer: &config.TCPLoadBalancerService{
+						Servers: []config.TCPServer{
+							{Address: "foobar"},
+						},
+					},
+				},
+			},
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			manager := NewManager(test.configs)
+
+			handler, err := manager.BuildTCP(context.Background(), test.serviceName)
+
+			if test.expectedError != "" {
+				if err == nil {
+					require.Error(t, err)
+				} else {
+					require.EqualError(t, err, test.expectedError)
+					require.Nil(t, handler)
+				}
+			} else {
+				require.NoError(t, err)
+				require.NotNil(t, handler)
+			}
+		})
+	}
+}