message: Extend the `SignatureCache` test with one assertion.
diff: @@ -112,5 +112,8 @@ mod tests {
  // Verify that era-0 signature is not cached anymore.
  assert!(!cache.known_signature(&block_hash, &sig_a.public_key));
  +
  + // Verify that era-1 signature is cached.
  + assert!(cache.known_signature(&block_hash, &sig_b.public_key));
  }
  }
  