routing: fix and enhance logging

channeldb/payment_control.go

@@ -424,7 +424,9 @@ func (p *PaymentControl) RegisterAttempt(paymentHash lntypes.Hash,
 		// Ensure we aren't sending more than the total payment amount.
 		sentAmt, _ := payment.SentAmt()
 		if sentAmt+amt > payment.Info.Value {
-			return ErrValueExceedsAmt
+			return fmt.Errorf("%w: attempted=%v, payment amount="+
+				"%v", ErrValueExceedsAmt, sentAmt+amt,
+				payment.Info.Value)
 		}
 
 		htlcsBucket, err := bucket.CreateBucketIfNotExists(

channeldb/payment_control_test.go

@@ -734,10 +734,7 @@ func TestPaymentControlMultiShard(t *testing.T) {
 		b := *attempt
 		b.AttemptID = 3
 		_, err = pControl.RegisterAttempt(info.PaymentIdentifier, &b)
-		if err != ErrValueExceedsAmt {
-			t.Fatalf("expected ErrValueExceedsAmt, got: %v",
-				err)
-		}
+		require.ErrorIs(t, err, ErrValueExceedsAmt)
 
 		// Fail the second attempt.
 		a := attempts[1]