### Question:
DataTypeStore { public List<DataType> getTopLevelDataTypes() { return all() .stream() .filter(DataType::isTopLevel) .collect(Collectors.toList()); }  DataType get(final String uuid); void index(final String uuid,
                      final DataType dataType); void clear(); int size(); List<DataType> getTopLevelDataTypes(); List<DataType> all(); void unIndex(final String uuid);  }### Answer:
@Test public void testGetTopLevelDataTypes() { final String secondUUID = "789"; final String thirdUUID = "012"; final DataType secondDataType = mock(DataType.class); final DataType thirdDataType = mock(DataType.class); when(secondDataType.isTopLevel()).thenReturn(true); store.index(secondUUID, secondDataType); store.index(thirdUUID, thirdDataType); final List<DataType> topLevelDataTypes = store.getTopLevelDataTypes(); assertEquals(topLevelDataTypes, singletonList(secondDataType)); }