htlcswitch: relay experimental endorsement signal with update_add_htlc

lntest/utils.go

@@ -282,3 +282,15 @@ func CalcStaticFeeBuffer(c lnrpc.CommitmentType, numHTLCs int) btcutil.Amount {
 
 	return feeBuffer.ToSatoshis()
 }
+
+// CustomRecordsWithUnendorsed copies the map of custom records and adds an
+// endorsed signal (replacing in the case of conflict) for assertion in tests.
+func CustomRecordsWithUnendorsed(
+	originalRecords lnwire.CustomRecords) map[uint64][]byte {
+
+	return originalRecords.MergedCopy(map[uint64][]byte{
+		uint64(lnwire.ExperimentalEndorsementType): {
+			lnwire.ExperimentalUnendorsed,
+		}},
+	)
+}