Add test for why identity hash does not work

pallets/relay-storage-roots/src/lib.rs

@@ -18,14 +18,14 @@
 //!
 //! This pallet stores the latest `MaxStorageRoots` relay storage roots, which can be used to
 //! verify state proofs against an old state of the relay chain.
-//! 
+//!
 //! This is useful when the proof needs to be generated by an end user, because
 //! by the time their transaction is included in a block, the latest relay
 //! block will probably have changed and therefore the proof will be invalid.
 //! To avoid that, we expect the user to generate a proof against the latest relay block stored
 //! in this pallet. This proof will then be valid as long as that relay block is not removed from
 //! here.
-//! 
+//!
 //! This pallet SHOULD NOT be used for data that can change quickly, because we allow the user to
 //! submit a proof of an old state. Therefore a valid proof does not imply that the current relay
 //! state is the expected one.

pallets/relay-storage-roots/src/tests.rs

@@ -71,3 +71,30 @@ fn oldest_items_are_removed_first() {
 			assert!(RelayStorageRoot::<Test>::get(0).is_none());
 		});
 }
+
+#[test]
+fn little_endian_keys_are_handled_properly() {
+	ExtBuilder::default()
+		.with_balances(vec![(ALICE, 15)])
+		.build()
+		.execute_with(|| {
+			// If the keys were stored in little endian, 256 would be removed right after being
+			// inserted
+			for i in 250..260 {
+				let relay_state = RelayChainState {
+					number: i,
+					state_root: H256::default(),
+				};
+				set_current_relay_chain_state(relay_state);
+				Pallet::<Test>::set_relay_storage_root();
+			}
+
+			// Only the first item has been removed
+			let keys = RelayStorageRootKeys::<Test>::get();
+			assert_eq!(
+				u32::try_from(keys.len()).unwrap(),
+				<Test as Config>::MaxStorageRoots::get()
+			);
+			assert_eq!(keys, vec![256, 257, 258, 259]);
+		});
+}