// Do not forget that we need every class to extends the abstract furnace classes or it won't work!
public class TestFurnace extends AbstractFurnaceBlock {
    public TestFurnace(Settings settings) {
        super(settings);
    }

    @Override
    public @Nullable BlockEntity createBlockEntity(BlockView world) {
        return new TestFurnaceBlockEntity();
    }

    @Override
    public void openScreen(World world, BlockPos pos, PlayerEntity player) {
        //This is called by the onUse method inside AbstractFurnaceBlock so
        //it is a little bit different of how you open the screen for normal container
        BlockEntity blockEntity = world.getBlockEntity(pos);
        if (blockEntity instanceof TestFurnaceBlockEntity) {
            player.openHandledScreen((NamedScreenHandlerFactory)blockEntity);
            // Optional: increment player's stat
            player.incrementStat(Stats.INTERACT_WITH_FURNACE);
        }
    }
}