routing: modify TestSendToRouteStructuredError to return non-second chance error

In this commit, we modify the existing `TestSendToRouteStructuredError`
test to return an error that doesn't trigger the second chance logic.
Otherwise, we'll get a nil failure result from the mission control
interpretation, meaning we won't exercise the full code path. Instead,
we use a terminal error to ensure that the expected code path is hit.

As is, this test will fail as a recent refactoring causes us to return a
`channeldb.FailureReason` error, since the newly added `handleSendError`
code path in the `SendToRoute` method will return the raw error, rather
than the `shardError`, which is of the expected type.

routing/router_test.go

@@ -2921,45 +2921,65 @@ func TestSendToRouteStructuredError(t *testing.T) {
 		t.Fatalf("unable to create route: %v", err)
 	}
 
-	// We'll modify the SendToSwitch method so that it simulates a failed
+	finalHopIndex := len(hops)
-	// payment with an error originating from the first hop of the route.
+	testCases := map[int]lnwire.FailureMessage{
-	// The unsigned channel update is attached to the failure message.
+		finalHopIndex: lnwire.NewFailIncorrectDetails(payAmt, 100),
+		1: &lnwire.FailFeeInsufficient{
+			Update: lnwire.ChannelUpdate{},
+		},
+	}
+
+	for failIndex, errorType := range testCases {
+		failIndex := failIndex
+		errorType := errorType
+
+		t.Run(fmt.Sprintf("%T", errorType), func(t *testing.T) {
+			// We'll modify the SendToSwitch method so that it
+			// simulates a failed payment with an error originating
+			// from the final hop in the route.
 			ctx.router.cfg.Payer.(*mockPaymentAttemptDispatcherOld).setPaymentResult(
 				func(firstHop lnwire.ShortChannelID) ([32]byte, error) {
 					return [32]byte{}, htlcswitch.NewForwardingError(
-				&lnwire.FailFeeInsufficient{
+						errorType, failIndex,
-					Update: lnwire.ChannelUpdate{},
+					)
-				}, 1,
+				},
 			)
-		})
 
-	// The payment parameter is mostly redundant in SendToRoute. Can be left
+			// The payment parameter is mostly redundant in
-	// empty for this test.
+			// SendToRoute.  Can be left empty for this test.
 			var payment lntypes.Hash
 
-	// Send off the payment request to the router. The specified route
+			// Send off the payment request to the router. The
-	// should be attempted and the channel update should be received by
+			// specified route should be attempted and the channel
-	// router and ignored because it is missing a valid signature.
+			// update should be received by router and ignored
+			// because it is missing a valid
+			// signature.
 			_, err = ctx.router.SendToRoute(payment, rt)
 
 			fErr, ok := err.(*htlcswitch.ForwardingError)
-	if !ok {
+			require.True(
-		t.Fatalf("expected forwarding error")
+				t, ok, "expected forwarding error, got: %T", err,
-	}
+			)
 
-	if _, ok := fErr.WireMessage().(*lnwire.FailFeeInsufficient); !ok {
+			require.IsType(
-		t.Fatalf("expected fee insufficient error")
+				t, errorType, fErr.WireMessage(),
-	}
+				"expected type %T got %T", errorType,
+				fErr.WireMessage(),
+			)
 
-	// Check that the correct values were used when initiating the payment.
+			// Check that the correct values were used when
+			// initiating the payment.
 			select {
 			case initVal := <-init:
 				if initVal.c.Value != payAmt {
-			t.Fatalf("expected %v, got %v", payAmt, initVal.c.Value)
+					t.Fatalf("expected %v, got %v", payAmt,
+						initVal.c.Value)
 				}
 			case <-time.After(100 * time.Millisecond):
 				t.Fatalf("initPayment not called")
 			}
+		})
+	}
 }
 
 // TestSendToRouteMultiShardSend checks that a 3-shard payment can be executed