tapchannel: use rfqmath in aux invoice manager prop tests

We also use the rfqmath library in the property based checks in order
to get rid of any discrepancies between the expected and actual values.

Author: GeorgeTsagk

tapchannel/aux_invoice_manager_test.go

@@ -271,28 +271,29 @@ func (m *mockHtlcModifierProperty) HtlcModifier(ctx context.Context,
 			continue
 		}
 
-		assetRate := lnwire.MilliSatoshi(
-			quote.AssetRate.Rate.ToUint64(),
-		)
-		msatPerBtc := float64(btcutil.SatoshiPerBitcoin * 1000)
-		unitValue := msatPerBtc / float64(assetRate)
-		assetUnits := lnwire.MilliSatoshi(htlc.Amounts.Val.Sum())
-
-		floatValue := float64(assetUnits) * unitValue
+		assetRate := quote.AssetRate.Rate
+		htlcAssets := htlc.Amounts.Val.Sum()
+		totalAssetAmount := rfqmath.NewBigIntFixedPoint(htlcAssets, 0)
 
-		assetValueMsat := lnwire.MilliSatoshi(floatValue)
+		amtPaid := rfqmath.UnitsToMilliSatoshi(
+			totalAssetAmount, assetRate,
+		)
 
 		acceptedMsat := lnwire.MilliSatoshi(0)
 		for _, htlc := range r.Invoice.Htlcs {
 			acceptedMsat += lnwire.MilliSatoshi(htlc.AmtMsat)
 		}
 
-		marginHtlcs := len(r.Invoice.Htlcs) + 1
-		marginMsat := lnwire.MilliSatoshi(
-			float64(marginHtlcs) * unitValue,
+		marginHtlcs := uint64(len(r.Invoice.Htlcs) + 1)
+		marginHtlcs++
+
+		marginAssetUnits := rfqmath.NewBigIntFixedPoint(marginHtlcs, 0)
+
+		marginMsat := rfqmath.UnitsToMilliSatoshi(
+			marginAssetUnits, assetRate,
 		)
 
-		totalMsatIn := marginMsat + assetValueMsat + acceptedMsat + 1
+		totalMsatIn := marginMsat + amtPaid + acceptedMsat + 1
 
 		invoiceValue := lnwire.MilliSatoshi(r.Invoice.ValueMsat)
 
@@ -301,9 +302,9 @@ func (m *mockHtlcModifierProperty) HtlcModifier(ctx context.Context,
 				m.t.Errorf("amt + accepted != invoice amt")
 			}
 		} else {
-			if assetValueMsat != res.AmtPaid {
+			if amtPaid != res.AmtPaid {
 				m.t.Errorf("unexpected final asset value, "+
-					"wanted %d, got %d", assetValueMsat,
+					"wanted %d, got %d", amtPaid,
 					res.AmtPaid)
 			}
 		}