Add test to block_store, export BlockAtSlotError

lighthouse/db/src/stores/block_store.rs

@@ -208,5 +208,8 @@ mod tests {
 
         let ssz = bs.block_at_slot(&hashes[4], 6).unwrap();
         assert_eq!(ssz, None);
+
+        let ssz = bs.block_at_slot(&Hash256::from("unknown".as_bytes()), 2);
+        assert_eq!(ssz, Err(BlockAtSlotError::UnknownBlock));
     }
 }

lighthouse/db/src/stores/mod.rs

@@ -7,7 +7,10 @@ mod block_store;
 mod pow_chain_store;
 mod validator_store;
 
-pub use self::block_store::BlockStore;
+pub use self::block_store::{
+    BlockStore,
+    BlockAtSlotError,
+};
 pub use self::pow_chain_store::PoWChainStore;
 pub use self::validator_store::{
     ValidatorStore,