EventHandler.java

    @SubscribeEvent
    public static void onAttachCapabilitiesTileEntity(AttachCapabilitiesEvent<TileEntity> event) {
        ResourceLocation location = new ResourceLocation(Ref.modinfo.modid, "test");
        if (event.getCapabilities().containsKey(location)) return;
        if (event.getObject() instanceof TileEntityChest) {
            event.addCapability(location, new CapProvider((IInventory) event.getObject()));
        }
    }