Add unit test for the fix

Test the case when eventing CR changes but NATS sub manager failed to
start

internal/controller/eventing/nats_test.go

@@ -188,6 +188,36 @@ func Test_reconcileNATSSubManager(t *testing.T) {
 			wantAssertCheck: true,
 			wantHashAfter:   int64(-7550677537009891034),
 		},
+		{
+			name: "it should update the subscription manager when the backend config changes" +
+				"but subscription manager failed to start",
+			givenIsNATSSubManagerStarted: false,
+			givenHashBefore:              int64(-8550677537009891034),
+			givenUpdateTest:              true,
+			givenNATSSubManagerMock: func() *submanagermocks.Manager {
+				jetStreamSubManagerMock := new(submanagermocks.Manager)
+				jetStreamSubManagerMock.On("Init", mock.Anything).Return(nil).Once()
+				jetStreamSubManagerMock.On("Start", mock.Anything, mock.Anything).Return(nil).Once()
+				return jetStreamSubManagerMock
+			},
+			givenEventingManagerMock: func() *managermocks.Manager {
+				emMock := new(managermocks.Manager)
+				emMock.On("GetBackendConfig").Return(givenBackendConfig).Twice()
+				return emMock
+			},
+			givenNatsConfigHandlerMock: func() *mocks.NatsConfigHandler {
+				nchMock := new(mocks.NatsConfigHandler)
+				nchMock.On("GetNatsConfig", mock.Anything, mock.Anything).Return(givenNATSConfig, nil)
+				return nchMock
+			},
+			givenManagerFactoryMock: func(subManager *submanagermocks.Manager) *subscriptionmanagermocks.ManagerFactory {
+				subManagerFactoryMock := new(subscriptionmanagermocks.ManagerFactory)
+				subManagerFactoryMock.On("NewJetStreamManager", mock.Anything, mock.Anything).Return(subManager).Once()
+				return subManagerFactoryMock
+			},
+			wantAssertCheck: true,
+			wantHashAfter:   int64(-7550677537009891034),
+		},
 	}
 
 	// run test cases