test/test: add lookup invoice to mock lightning client

Track the invoices we create with AddInvoice so that we can
realistically lookup and settle with the mock.

test/lightning_client_mock.go

@@ -7,6 +7,8 @@ import (
 	"sync"
 	"time"
 
+	"github.com/lightningnetwork/lnd/channeldb"
+
 	"github.com/btcsuite/btcd/btcec"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/btcsuite/btcutil"
@@ -125,9 +127,39 @@ func (h *mockLightningClient) AddInvoice(ctx context.Context,
 		return lntypes.Hash{}, "", err
 	}
 
+	// Add the invoice we have created to our mock's set of invoices.
+	h.lnd.Invoices[hash.String()] = &lndclient.Invoice{
+		Preiamge:       nil,
+		Hash:           hash,
+		PaymentRequest: payReqString,
+		Amount:         in.Value,
+		CreationDate:   time.Now(),
+		State:          channeldb.ContractOpen,
+		IsKeysend:      false,
+	}
+
 	return hash, payReqString, nil
 }
 
+// LookupInvoice looks up an invoice in the mock's set of stored invoices.
+// If it is not found, this call will fail. Note that these invoices should
+// be settled using settleInvoice to have a preimage, settled state and settled
+// date set.
+func (h *mockLightningClient) LookupInvoice(_ context.Context,
+	// nolint: interfacer
+	hash lntypes.Hash) (*lndclient.Invoice, error) {
+
+	h.lnd.lock.Lock()
+	defer h.lnd.lock.Unlock()
+
+	inv, ok := h.lnd.Invoices[hash.String()]
+	if !ok {
+		return nil, fmt.Errorf("invoice: %x not found", hash)
+	}
+
+	return inv, nil
+}
+
 // ListTransactions returns all known transactions of the backing lnd node.
 func (h *mockLightningClient) ListTransactions(
 	ctx context.Context) ([]*wire.MsgTx, error) {

test/lnd_services_mock.go

@@ -69,6 +69,7 @@ func NewMockLnd() *LndMockServices {
 		NodePubkey:         testNodePubkey,
 		Signature:          testSignature,
 		SignatureMsg:       testSignatureMsg,
+		Invoices:           make(map[string]*lndclient.Invoice),
 	}
 
 	lightningClient.lnd = &lnd
@@ -158,6 +159,10 @@ type LndMockServices struct {
 
 	Transactions []*wire.MsgTx
 
+	// Invoices is a set of invoices that have been created by the mock,
+	// keyed by hash string.
+	Invoices map[string]*lndclient.Invoice
+
 	WaitForFinished func()
 
 	lock sync.Mutex