test: ensure the WaitForBlockchainSync grouting always exits

This commit fixes a minor bug in the goroutine that’s launched to check
the sync status of a particular node. Previously, the goroutine could
end up infinitely stuck on a send as once the chain has been detected
as synced, it didn't exit.

We fix this now by ensure that the goroutine always terminates after
the initial notification to the caller. Additionally, we not ensure
that both the internal and exterior goroutine are both reading off of
the peer’s quit channel.

lnd_test.go

@@ -416,7 +416,7 @@ func testDisconnectingTargetPeer(net *networkHarness, t *harnessTest) {
 
 	// At this point, the channel should be fully opened and there should
 	// be no pending channels remaining for either node.
-	time.Sleep(time.Millisecond * 3000)
+	time.Sleep(time.Millisecond * 300)
 	ctxt, _ = context.WithTimeout(ctxb, timeout)
 
 	assertNumOpenChannelsPending(ctxt, t, net.Alice, net.Bob, 0)

networktest.go

@@ -600,34 +600,46 @@ func (l *lightningNode) WaitForNetworkChannelClose(ctx context.Context,
 	}
 }
 
-// WaitForBlockchainSync will block until node synchronizes its blockchain
+// WaitForBlockchainSync will block until the target nodes has fully
+// synchronized with the blockchain. If the passed context object has a set
+// timeout, then the goroutine will continually poll until the timeout has
+// elapsed. In the case that the chain isn't synced before the timeout is up,
+// then this function will return an error.
 func (l *lightningNode) WaitForBlockchainSync(ctx context.Context) error {
 	errChan := make(chan error, 1)
 	retryDelay := time.Millisecond * 100
+
 	go func() {
 		for {
 			select {
 			case <-ctx.Done():
-				break
+			case <-l.quit:
+				return
 			default:
 			}
+
 			getInfoReq := &lnrpc.GetInfoRequest{}
 			getInfoResp, err := l.GetInfo(ctx, getInfoReq)
 			if err != nil {
 				errChan <- err
-				break
+				return
 			}
 			if getInfoResp.SyncedToChain {
 				errChan <- nil
+				return
 			}
+
 			select {
 			case <-ctx.Done():
-				break
+				return
 			case <-time.After(retryDelay):
 			}
 		}
 	}()
+
 	select {
+	case <-l.quit:
+		return nil
 	case err := <-errChan:
 		return err
 	case <-ctx.Done():
@@ -1033,7 +1045,10 @@ func (n *networkHarness) OpenChannel(ctx context.Context,
 	srcNode, destNode *lightningNode, amt btcutil.Amount,
 	pushAmt btcutil.Amount, numConfs uint32) (lnrpc.Lightning_OpenChannelClient, error) {
 
-	// Wait until srcNode and destNode have blockchain synced
+	// Wait until srcNode and destNode have the latest chain synced.
+	// Otherwise, we may run into a check within the funding manager that
+	// prevents any funding workflows from being kicked off if the chain
+	// isn't yet synced.
 	if err := srcNode.WaitForBlockchainSync(ctx); err != nil {
 		return nil, fmt.Errorf("Unable to sync srcNode chain: %v", err)
 	}