@Test
 @SuppressWarnings("unchecked")
 public void findConnectionsToUsers() {
   connectionFactoryRegistry.addConnectionFactory(new TestTwitterConnectionFactory());
   insertTwitterConnection();
   insertFacebookConnection();
   insertFacebookConnection2();
   MultiValueMap<String, String> providerUsers = new LinkedMultiValueMap<>();
   providerUsers.add("facebook", "10");
   providerUsers.add("facebook", "9");
   providerUsers.add("twitter", "1");
   MultiValueMap<String, Connection<?>> connectionsForUsers =
       connectionRepository.findConnectionsToUsers(providerUsers);
   assertEquals(2, connectionsForUsers.size());
   assertEquals("10", connectionsForUsers.getFirst("facebook").getKey().getProviderUserId());
   assertFacebookConnection(
       (Connection<TestFacebookApi>) connectionsForUsers.get("facebook").get(1));
   assertTwitterConnection((Connection<TestTwitterApi>) connectionsForUsers.getFirst("twitter"));
 }
 @Test(expected = IllegalArgumentException.class)
 public void findConnectionsToUsersEmptyInput() {
   MultiValueMap<String, String> providerUsers = new LinkedMultiValueMap<>();
   connectionRepository.findConnectionsToUsers(providerUsers);
 }
 @Test
 public void findConnectionsToUsersEmptyResult() {
   MultiValueMap<String, String> providerUsers = new LinkedMultiValueMap<>();
   providerUsers.add("facebook", "1");
   assertTrue(connectionRepository.findConnectionsToUsers(providerUsers).isEmpty());
 }