adds test

relayer/relays/beacon/header/header.go

@@ -560,6 +560,7 @@ func (h *Header) findLatestCheckPoint(slot uint64) (state.FinalizedHeader, error
 	// https://github.com/paritytech/polkadot-sdk/blob/master/bridges/snowbridge/pallets/ethereum-client/src/lib.rs#L75
 	for {
 		index = (index - 1 + totalStates) % totalStates
+		// We have searched the whole ringbuffer and could not find the header.
 		if index == startIndex {
 			log.WithError(err).Debug("unable to find a relevant on-chain header, max iterations reached")
 			break
@@ -584,6 +585,7 @@ func (h *Header) findLatestCheckPoint(slot uint64) (state.FinalizedHeader, error
 		if beaconState.BeaconSlot > slot && beaconState.BeaconSlot < slot+syncCommitteePeriod {
 			return beaconState, nil
 		}
+
 	}
 
 	return beaconState, fmt.Errorf("no checkpoint on chain for slot %d", slot)

relayer/relays/beacon/header/header_test.go

@@ -427,6 +427,12 @@ func TestFindLatestCheckPoint(t *testing.T) {
 	assert.Equal(t, headerIndex4, header.BeaconBlockRoot)
 	assert.Equal(t, uint64(46), header.BeaconSlot)
 
+	// Check that the first item in the ringbuffer can be found
+	header, err = h.findLatestCheckPoint(43)
+	assert.NoError(t, err)
+	assert.Equal(t, headerIndex4, header.BeaconBlockRoot)
+	assert.Equal(t, uint64(46), header.BeaconSlot)
+
 	// Check last finalized state index outside of the circular array does not cause an infinite loop
 	mockWriter.LastFinalizedStateIndex = types.U32((maxRedundancy * settings.EpochsPerSyncCommitteePeriod) + 50)
 	header, err = h.findLatestCheckPoint(40)