### Question:
PingLoopbackLink extends AbstractLink<LinkSettings> implements Link<LinkSettings> { @Override public void registerLinkHandler(LinkHandler ilpDataHandler) throws LinkHandlerAlreadyRegisteredException { throw new RuntimeException( "PingLoopback links never have incoming data, and thus should not have a registered DataHandler." ); } PingLoopbackLink(
      final Supplier<InterledgerAddress> operatorAddressSupplier, final LinkSettings linkSettings
  ); @Override void registerLinkHandler(LinkHandler ilpDataHandler); @Override InterledgerResponsePacket sendPacket(final InterledgerPreparePacket preparePacket); @Override String toString(); static final String LINK_TYPE_STRING; static final LinkType LINK_TYPE; static final InterledgerFulfillment PING_PROTOCOL_FULFILLMENT; static final InterledgerCondition PING_PROTOCOL_CONDITION; }### Answer:
@Test(expected = RuntimeException.class) public void registerLinkHandler() { try { link.registerLinkHandler(incomingPreparePacket -> null); } catch (Exception e) { assertThat(e.getMessage()).isEqualTo( "PingLoopback links never have incoming data, and thus should not have a registered DataHandler."); throw e; } }