[FAB-4854] Harden TestMsgStoreExpiration test

Refactor TestMsgStoreExpiration test to assert for membership while
leveraging context with timeout and verify membership simultaneously
rather than interating over peer instances to check for required number
of nodes in view.

Change-Id: Ib165be64b3fd7977356b87b8ee4d978eb0da91cc
Signed-off-by: Artem Barger <bartem@il.ibm.com>

gossip/discovery/discovery_test.go

@@ -1206,15 +1206,30 @@ func stopInstances(t *testing.T, instances []*gossipInstance) {
 }
 
 func assertMembership(t *testing.T, instances []*gossipInstance, expectedNum int) {
-	fullMembership := func() bool {
-		for _, inst := range instances {
-			if len(inst.GetMembership()) != expectedNum {
-				return false
+	wg := sync.WaitGroup{}
+	wg.Add(len(instances))
+
+	ctx, cancelation := context.WithTimeout(context.Background(), timeout)
+	defer cancelation()
+
+	for _, inst := range instances {
+		go func(ctx context.Context, i *gossipInstance) {
+			defer wg.Done()
+			for {
+				select {
+				case <-ctx.Done():
+					return
+				case <-time.After(timeout / 10):
+					if len(i.GetMembership()) == expectedNum {
+						return
+					}
+				}
 			}
-		}
-		return true
+		}(ctx, inst)
 	}
-	waitUntilOrFail(t, fullMembership)
+
+	wg.Wait()
+	assert.NoError(t, ctx.Err(), "Timeout expired!")
 }
 
 func portsOfMembers(members []NetworkMember) []int {