better handling of test multicast listener initialisation errors

We handle that error explicitly in all cases and point out the common
cause, namely the absence of a default multicast interface.

Closes #481.

nameserver/mdns_client_test.go

@@ -73,15 +73,16 @@ func RunLocalMulticastServer() (*dns.Server, error) {
 }
 
 func setup(t *testing.T) (*MDNSClient, *dns.Server, error) {
+	server, err := RunLocalMulticastServer()
+	if err != nil {
+		t.Fatalf("Unable to run test server: %s. No default multicast interface?", err)
+	}
+
 	mdnsClient, err := NewMDNSClient()
 	wt.AssertNoErr(t, err)
 	err = mdnsClient.Start(nil)
 	wt.AssertNoErr(t, err)
 
-	server, err := RunLocalMulticastServer()
-	if err != nil {
-		t.Fatalf("Unable to run test server: %s", err)
-	}
 	return mdnsClient, server, err
 }
 

nameserver/mdns_server_test.go

@@ -42,11 +42,6 @@ func TestServerSimpleQuery(t *testing.T) {
 	ip, _, _ := net.ParseCIDR(testAddr1)
 	zone.AddRecord(containerID, testName, ip)
 
-	mdnsServer, err := NewMDNSServer(zone)
-	wt.AssertNoErr(t, err)
-	err = mdnsServer.Start(nil, DefaultLocalDomain)
-	wt.AssertNoErr(t, err)
-
 	var receivedAddr net.IP
 	var receivedName string
 	var recvChan chan interface{}
@@ -70,7 +65,9 @@ func TestServerSimpleQuery(t *testing.T) {
 
 	// Implement a minimal listener for responses
 	multicast, err := LinkLocalMulticastListener(nil)
-	wt.AssertNoErr(t, err)
+	if err != nil {
+		t.Fatalf("Unable to run test server: %s. No default multicast interface?", err)
+	}
 
 	handleMDNS := func(w dns.ResponseWriter, r *dns.Msg) {
 		// Only handle responses here
@@ -93,6 +90,11 @@ func TestServerSimpleQuery(t *testing.T) {
 	go listener.ActivateAndServe()
 	defer listener.Shutdown()
 
+	mdnsServer, err := NewMDNSServer(zone)
+	wt.AssertNoErr(t, err)
+	err = mdnsServer.Start(nil, DefaultLocalDomain)
+	wt.AssertNoErr(t, err)
+
 	time.Sleep(100 * time.Millisecond) // Allow for server to get going
 
 	reset()

nameserver/server_test.go

@@ -22,12 +22,19 @@ var (
 	testPort = 17625
 )
 
-func setupForTest() {
+func setupForTest(t *testing.T) {
+	// fail early if we cannot find a default multicast interface
+	multicast, err := LinkLocalMulticastListener(nil)
+	if err != nil {
+		t.Fatalf("Unable to create multicast listener: %s. No default multicast interface?", err)
+	}
+	multicast.Close()
+
 	testPort++
 }
 
 func TestUDPDNSServer(t *testing.T) {
-	setupForTest()
+	setupForTest(t)
 	const (
 		successTestName = "test1.weave.local."
 		failTestName    = "test2.weave.local."
@@ -110,7 +117,7 @@ func TestUDPDNSServer(t *testing.T) {
 }
 
 func TestTCPDNSServer(t *testing.T) {
-	setupForTest()
+	setupForTest(t)
 	const (
 		numAnswers   = 512
 		nonLocalName = "weave.works."