Test: Weight Validation

test.rs

// Simple test to validate weights resulting from weight functions, generated by benchmarking, against various known limits.
//
// NOTE: this is simply to provide a rough indication of dispatchable weights in relation to block limits, which can be useful for:
// - ensuring a dispatchable does not exceed block, max extrinsic limits and regression testing
// - evaluating if some optimisation results in net reduction in weight usage
// - getting a feel for weights early during pallet development and monitoring through optimisation
//
// Is only as good as the corresponding runtime configuration (i.e. test placed within pallet with mock runtime vs placed within runtime with actual runtime config).
// Also ensure the limits are relevant to your implementation, they may have changed with newer versions and will definitely change with async backing.
// Finally, it uses the generated weight functions directly and therefore does not cater to any post-dispatch weight adjustment resulting from a dispatchable.
#[test]
fn weights() {
	use crate::weights::WeightInfo;
	use frame_support::weights::{constants::WEIGHT_REF_TIME_PER_SECOND, Weight};
	// max block: 0.5s compute with 12s average block time
	const MAX_BLOCK_REF_TIME: u64 = WEIGHT_REF_TIME_PER_SECOND.saturating_div(2); // https://github.com/paritytech/cumulus/blob/98e68bd54257b4039a5d5b734816f4a1b7c83a9d/parachain-template/runtime/src/lib.rs#L221
	const MAX_BLOCK_POV_SIZE: u64 = 5 * 1024 * 1024; // https://github.com/paritytech/polkadot/blob/ba1f65493d91d4ab1787af2fd6fe880f1da90586/primitives/src/v4/mod.rs#L384
	const MAX_BLOCK_WEIGHT: Weight = Weight::from_parts(MAX_BLOCK_REF_TIME, MAX_BLOCK_POV_SIZE);
	// max extrinsics: 75% of block
	const NORMAL_DISPATCH_RATIO: Perbill = Perbill::from_percent(75); // https://github.com/paritytech/cumulus/blob/d20c4283fe85df0c1ef8cb7c9eb7c09abbcbfa31/parachain-template/runtime/src/lib.rs#L218
	let max_total_extrinsics = MAX_BLOCK_WEIGHT * NORMAL_DISPATCH_RATIO;
	// max extrinsic: max total extrinsics less average on_initialize ratio and less base extrinsic weight
	const AVERAGE_ON_INITIALIZE_RATIO: Perbill = Perbill::from_percent(5); // https://github.com/paritytech/cumulus/blob/d20c4283fe85df0c1ef8cb7c9eb7c09abbcbfa31/parachain-template/runtime/src/lib.rs#L214
	const BASE_EXTRINSIC: Weight =
		Weight::from_parts(WEIGHT_REF_TIME_PER_NANOS.saturating_mul(125_000), 0); // https://github.com/paritytech/cumulus/blob/d20c4283fe85df0c1ef8cb7c9eb7c09abbcbfa31/parachain-template/runtime/src/weights/extrinsic_weights.rs#L26
	let max_extrinsic_weight = max_total_extrinsics
		.saturating_sub(MAX_BLOCK_WEIGHT * AVERAGE_ON_INITIALIZE_RATIO)
		.saturating_sub(BASE_EXTRINSIC);
	assert_eq!(max_extrinsic_weight, Weight::from_parts(349_875_000_000, 3_670_016));

	println!("max block weight: {MAX_BLOCK_WEIGHT}");
	println!("max total extrinsics weight: {max_total_extrinsics}");
	println!("max extrinsic weight: {max_extrinsic_weight}\n");

	let mut total = Weight::zero();
	for (function, weight) in vec![
		// Examples: call available weight functions with various parameters (as applicable) to gauge weight usage in comparison to limits
		("do_something", Weights::do_something()),
		("do_some_things (zero)", Weights::do_some_things(0)),
		("do_some_things (max)", Weights::do_some_things(<Test as Config>::MaxThings::get())),
	] {
		println!("{function}: {weight:?}",);
		println!(
			"\tpercentage of max extrinsic weight: {:.2}% (ref_time), {:.2}% (proof_size)",
			(weight.ref_time() as f64 / max_extrinsic_weight.ref_time() as f64) * 100.0,
			(weight.proof_size() as f64 / max_extrinsic_weight.proof_size() as f64) * 100.0,
		);
		println!(
			"\tmax tx per block: {} (ref_time), {} (proof_size)",
			max_extrinsic_weight.ref_time() / weight.ref_time(),
			max_extrinsic_weight.proof_size() / weight.proof_size()
		);
		assert!(weight.all_lt(max_extrinsic_weight));

		total += weight;
	}

	// output total weight, useful for evaluating net weight changes when optimising
	println!("\ntotal weight: {total:?}");
}