Ease implementation of mock for pallets.

[gui1117]

Currently there is very few provided function for doing some mocking of pallets.

People almost always implement some function like:

fn run_to_block(n: u32) {
	assert!(System::block_number() < n);
	while System::block_number() < n {
		let block_number = System::block_number();
		AllPalletsWithSystem::on_finalize(block_number);
		System::set_block_number(block_number + 1);
		maybe_new_session(block_number + 1);
		AllPalletsWithSystem::on_initialize(block_number + 1);
	}
}

Those function are sometime incomplete implementation of state transition.

I think maybe we can make use of frame_executive::Executive in tests, or provide some helper to avoid having to implement those function everywhere.

[AurevoirXavier]

Indeed, we need this. There are too many such duplicated code.

@kianenigma Could you draft a simple "task list"? Where could be the best entry point to "inject" such run_to_block logic?

I'd love to take this issue.

[kianenigma]

Option1: we can alter construct_runtime and/or the new version #[runtime] to spit out this function for you.
Option2: Have this function in frame_system/frame_executive with a #[cfg(feature = "std")] and it takes in things like AllPalletsWithSystem as generic argument.

Second is much better as it does not involve magically generated code.