Fix goroutine leak in server test.

In `TestResponseHandler`, the test runs the server in a goroutine,
but doesn't guarantee that the goroutine completes before the end of
the test. In addition to simply leaking the goroutine, this can panic
if there is an error after the test completes. In that case, it is
unnecessarily hard to debug.

Signed-off-by: James Peach <jpeach@apache.org>

pkg/server/v3/server_test.go

@@ -33,6 +33,7 @@ import (
 	"github.com/envoyproxy/go-control-plane/pkg/server/stream/v3"
 	"github.com/envoyproxy/go-control-plane/pkg/server/v3"
 	"github.com/envoyproxy/go-control-plane/pkg/test/resource/v3"
+	"github.com/stretchr/testify/assert"
 )
 
 type mockConfigWatcher struct {
@@ -303,13 +304,17 @@ func TestServerShutdown(t *testing.T) {
 func TestResponseHandlers(t *testing.T) {
 	for _, typ := range testTypes {
 		t.Run(typ, func(t *testing.T) {
+			done := make(chan struct{})
+			ctx, cancel := context.WithCancel(context.Background())
+
 			config := makeMockConfigWatcher()
 			config.responses = makeResponses()
-			s := server.NewServer(context.Background(), config, server.CallbackFuncs{})
+			s := server.NewServer(ctx, config, server.CallbackFuncs{})
 
 			// make a request
 			resp := makeMockStream(t)
 			resp.recv <- &discovery.DiscoveryRequest{Node: node, TypeUrl: typ}
+
 			go func(rType string) {
 				var err error
 				switch rType {
@@ -332,9 +337,8 @@ func TestResponseHandlers(t *testing.T) {
 				case opaqueType:
 					err = s.StreamAggregatedResources(resp)
 				}
-				if err != nil {
-					t.Errorf("Stream() => got %v, want no error", err)
-				}
+				assert.NoError(t, err)
+				close(done)
 			}(typ)
 
 			// check a response
@@ -347,6 +351,9 @@ func TestResponseHandlers(t *testing.T) {
 			case <-time.After(1 * time.Second):
 				t.Fatalf("got no response")
 			}
+
+			cancel()
+			<-done
 		})
 	}
 }