PVF: add test-utils feature and remove #[doc(hidden)]

[mrcnski]

ISSUE

Overview

In the PVF modules we export a good amount of stuff for only testing in other crates. #[cfg(test)] does not expose code across crates so we use #[doc(hidden)] for exposing test methods. However it's unfortunate that test code ends up in production builds this way. This can be done in a nicer way by adding a new feature.

Credit to @s0me0ne-unkn0wn here.

[jpserrat]

Hi @mrcnski, I want to work on this, just have a few questions.
The ones that I would have to change to feature would be this ones:

polkadot/node/core/pvf/src/worker_intf.rs

Lines 42 to 43 in e0ed7e8

	#[doc(hidden)]
	pub async fn spawn_with_program_path(

polkadot/node/core/pvf/common/src/lib.rs

Lines 33 to 34 in e0ed7e8

	#[doc(hidden)]
	pub mod tests {

polkadot/node/core/pvf/common/src/pvf.rs

Lines 87 to 88 in e0ed7e8

	#[doc(hidden)]
	pub fn from_discriminator_and_timeout(num: u32, timeout: Duration) -> Self {

polkadot/node/core/pvf/common/src/pvf.rs

Lines 99 to 100 in e0ed7e8

	#[doc(hidden)]
	pub fn from_discriminator(num: u32) -> Self {

polkadot/node/core/pvf/common/src/pvf.rs

Lines 105 to 106 in e0ed7e8

	#[doc(hidden)]
	pub fn from_discriminator_precheck(num: u32) -> Self {

polkadot/node/core/pvf/src/lib.rs

Lines 100 to 101 in e0ed7e8

	#[doc(hidden)]
	pub mod testing;

polkadot/node/core/pvf/src/lib.rs

Lines 103 to 105 in e0ed7e8

	// Used by `decl_puppet_worker_main!`.
	#[doc(hidden)]
	pub use sp_tracing;

Is that correct?
May I assume that all functions using them are test functions?

[s0me0ne-unkn0wn]

from_discriminator_* are definitely test-only functions (they create meaningless dummy objects just for tests), spawn_with_program_path is documented as test-only, but I'd check it twice just in case.

Also, I'm not sure if the CI scripts in scripts/ have to be patched to make use of the new feature (see test.yml in the first place), or it will just work as-is with cargo test.

[ggwpez]

Yea I am using the dev-dependency feature approach in another project and it works fine so far. Should be much better than #[test] anyway.

[s0me0ne-unkn0wn]

@jpserrat as far as I see, the spawn_with_program_path is used in production code but just wouldn't need to be publicly exposed if it wasn't needed for integration tests. So it's okay to just keep #[doc(hidden)] and leave it alone.

[mrcnski]

Would also be nice to gate the puppet worker behind the new feature (as anything related to the puppet worker is test-only). I think it can be done with required-features in the [[bin]] section in Cargo.toml. This would improve compile times as we wouldn't always build the puppet worker on non-test builds. 🙌

[jpserrat]

Thanks a lot for the help and suggestions with this one. Let me know if there are some improvements to be made.