For some test plans, it is useful to pass information from one instance to another. In addition to direct network connectivity, test plans can pass information between instances using the Testground sync service.
In this tutorial, we will explore typed message passing through the Testground sync service.
Lets create a plan in which one of the plans produces a struct which is re-constructed on the distant end. First, I'll show short snippets with the relevant information, and the whole test plan will be shown at the end.
Setting up thetopic
Transferrable is the value type we will be transferring.
typeTransferrablestruct { Name string FavoriteSport int CareWhoKnows bool}
The value will be transferred over a topic. Think of the topic as a named and typed channel for transferring values between plan instances. This topic is named transfer-key and the value type I expect to get out of it is pointer to Transferrable.
st := sync.NewTopic("transfer-key", &Transferrable{})
Publishing to a topic
To write to a topic, create a bounded client and use it to publish to the topic we have just defined.
This question is left up to the plan writer, and certainly different situations will call for different implementations. In this example, all the plans will publish and all will subscribe, but there are scenarios where this is inappropriate.
Full Example
packagemainimport ("context""fmt""math/rand""time""github.com/testground/sdk-go/run""github.com/testground/sdk-go/runtime""github.com/testground/sdk-go/sync")typeSportintconst ( football Sport=iota tennis hockey golf)func (s Sport) String() string {return [...]string{"football", "tennis", "hockey", "golf"}[s]}typeTransferrablestruct { Name string FavoriteSport Sport CareWhoKnows bool}func (t *Transferrable) String() string { msg := fmt.Sprintf("%s: I like %s", t.Name, t.FavoriteSport)if t.CareWhoKnows {return msg +" and I really care!" }return msg +" and I don't care who knows!"}funcmain() { run.Invoke(test)}functest(runenv *runtime.RunEnv) error { rand.Seed(time.Now().UnixNano()) ctx := context.Background() client := sync.MustBoundClient(ctx, runenv)defer client.Close() st := sync.NewTopic("transfer-key", &Transferrable{})// Configure the test myName := fmt.Sprintf("Guy#%d", rand.Int()%100) mySport := Sport(rand.Int() %4) howMany := runenv.TestInstanceCount// Publish my entry client.Publish(ctx, st, &Transferrable{myName, mySport, false})// Wait until all instances have published entries readyState := sync.State("ready") client.MustSignalEntry(ctx, readyState)<-client.MustBarrier(ctx, readyState, howMany).C// Subscribe to the `transfer-key` topic tch :=make(chan*Transferrable) client.Subscribe(ctx, st, tch)for i :=0; i < howMany; i++ { t :=<-tch runenv.RecordMessage("%s", t) }returnnil}
Run with multiple instances:
$ testground run single -p quickstart -t quickstart -b exec:go -r local:exec -i 4
?> Notice that instances is set to 4. Four instances will run at the same time.