Add unit tests for the equivocation detection loop (#2571)

* Add unit tests for the equivocation detection loop

* clippy

* use std::future::pending()

bridges/primitives/header-chain/src/justification/verification/mod.rs

@@ -143,6 +143,7 @@ pub enum PrecommitError {
 }
 
 /// The context needed for validating GRANDPA finality proofs.
+#[derive(RuntimeDebug)]
 pub struct JustificationVerificationContext {
 	/// The authority set used to verify the justification.
 	pub voter_set: VoterSet<AuthorityId>,