lnwallet: introduce default routing fee calculation

lnwallet/parameters_test.go

@@ -1,13 +1,52 @@
 package lnwallet
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/btcsuite/btcutil"
 	"github.com/lightningnetwork/lnd/input"
+	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/stretchr/testify/require"
 )
 
+// TestDefaultRoutingFeeLimitForAmount tests that we use the correct default
+// routing fee depending on the amount.
+func TestDefaultRoutingFeeLimitForAmount(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		amount        lnwire.MilliSatoshi
+		expectedLimit lnwire.MilliSatoshi
+	}{
+		{
+			amount:        1,
+			expectedLimit: 1,
+		},
+		{
+			amount:        50_000,
+			expectedLimit: 50_000,
+		},
+		{
+			amount:        50_001,
+			expectedLimit: 2_500,
+		},
+		{
+			amount:        5_000_000_000,
+			expectedLimit: 250_000_000,
+		},
+	}
+
+	for _, test := range tests {
+		test := test
+
+		t.Run(fmt.Sprintf("%d sats", test.amount), func(t *testing.T) {
+			feeLimit := DefaultRoutingFeeLimitForAmount(test.amount)
+			require.Equal(t, test.expectedLimit, feeLimit)
+		})
+	}
+}
+
 // TestDustLimitForSize tests that we receive the expected dust limits for
 // various script types from btcd's GetDustThreshold function.
 func TestDustLimitForSize(t *testing.T) {