### Question:
CompositeDataHandlersLoader implements DataHandlersLoader { @Override public Map<String, ? extends DataHandler> dataHandlers(final Set<String> filter) { final ImmutableSet.Builder<String> filterBuilder = ImmutableSet.<String>builder().addAll(filter); final ImmutableMap.Builder<String, DataHandler> dataHandlers = ImmutableMap.builder(); for (final DataHandlersLoader delegate : delegateList) { dataHandlers.putAll(delegate.dataHandlers(filterBuilder.build())); filterBuilder.addAll(dataHandlers.build().keySet()); } return dataHandlers.build(); } CompositeDataHandlersLoader(final List<DataHandlersLoader> delegateList); @Override Map<String, ? extends DataHandler> dataHandlers(final Set<String> filter);  }### Answer:
@Test public void testDataHandlersLoading() { final CompositeDataHandlersLoader dataHandlersLoader = new CompositeDataHandlersLoader( ImmutableList.of( new DefaultDataHandlersLoader(), new DefaultDataHandlersLoader(), new DefaultDataHandlersLoader() ) ); final Map<String, ? extends DataHandler> dataHandlersMap = dataHandlersLoader.dataHandlers(); assertThat(dataHandlersMap.keySet(), equalTo(TEST_MAPPINGS)); }