[1.15.2] Append a Jigsaw pool

[Dzuchun]

For a while, I`m trying to add a custom villager house to a village house pool, so it could be generated in villages as vanilla houses do.

I looked through a vanilla code, this forum, googled it, checked some other mod sources, and actually all I've found about that is to:
(copy+paste+renaming from net.minecraft.world.gen.feature.structure.PlainsVillagePools)

JigsawManager.REGISTRY.register(new JigsawPattern(
  new ResourceLocation("village/plains/houses"),
  new ResourceLocation("village/plains/terminators"),
  ImmutableList.of(
    new Pair<>(new SingleJigsawPiece("testmod:test_structure"), 10) //10 is to increase probabillity, as I've understood related code
  ), PlacementBehaviour.RIGID ));

, invoked within setupWorldGen: (actually, in a static initializer of a class, whose method is called in setupWorldGen; I`m sure the code is executed, due to my special log message sent)

@SubscribeEvent 
public static void commonSetup(final FMLCommonSetupEvent event) {
	DeferredWorkQueue.runLater( ()-> setupWorldGen()); 
}

with valid NBT structure file stored at data/testmod/structures.

But I couldn't find my house within newly-generated villages.

This structure includes single Jigsaw block, configured as one in vanilla structure village/plains/houses/plains_small_house_1 except "Turns into" value, which i left as minecraft:air.

Structure file is definitely valid, because I succeed it`s generation as a ScatteredStructure randomly in the world.

Actually, the question is: what is actually done to properly add JigsawPiece to a pool?

I'd be graceful for any help here or useful links to guides, documentations, etc.

 

Sadly, provision of a full source code would be very uncultured, because It`s my first mod, so a source code looks like hell.

(But if You want to check it out - here it is)

 

I`m sorry for any misunderstanding and mistakes, due to I`m very new to forge.

Thanks again for help.

Edited May 5, 2020 by Dzuchun
(repaired link)