fix race in chat example test

- t.Parallel() doesn't guarantee parallel execution
- moved goroutine so the test can execute independently

example/chat/chat_test.go

@@ -2,7 +2,6 @@ package chat
 
 import (
 	"net/http/httptest"
-	"sync"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -13,40 +12,70 @@ import (
 func TestChat(t *testing.T) {
 	srv := httptest.NewServer(handler.GraphQL(MakeExecutableSchema(New())))
 	c := client.New(srv.URL)
-	var wg sync.WaitGroup
-	wg.Add(1)
 
 	t.Run("subscribe to chat events", func(t *testing.T) {
 		t.Parallel()
 
 		sub := c.Websocket(`subscription { messageAdded(roomName:"#gophers") { text createdBy } }`)
 		defer sub.Close()
 
-		wg.Done()
-		var resp struct {
+		postErrCh := make(chan error)
+		go func() {
+			var resp interface{}
+			// can't call t.Fatal from separate goroutine, so we return to the err chan for later
+			err := c.Post(`mutation { 
+				a:post(text:"Hello!", roomName:"#gophers", username:"vektah") { id } 
+				b:post(text:"Whats up?", roomName:"#gophers", username:"vektah") { id } 
+			}`, &resp)
+			if err != nil {
+				// only push this error if non-nil
+				postErrCh <- err
+			}
+		}()
+
+		type resp struct {
 			MessageAdded struct {
 				Text      string
 				CreatedBy string
 			}
 		}
-		require.NoError(t, sub.Next(&resp))
-		require.Equal(t, "Hello!", resp.MessageAdded.Text)
-		require.Equal(t, "vektah", resp.MessageAdded.CreatedBy)
 
-		require.NoError(t, sub.Next(&resp))
-		require.Equal(t, "Whats up?", resp.MessageAdded.Text)
-		require.Equal(t, "vektah", resp.MessageAdded.CreatedBy)
-	})
+		// Contains the result of a `sub.Next` call
+		type subMsg struct {
+			resp
+			err error
+		}
 
-	t.Run("post two messages", func(t *testing.T) {
-		t.Parallel()
+		subCh := make(chan subMsg)
+		go func() {
+			var msg subMsg
+
+			msg.err = sub.Next(&msg.resp)
+			subCh <- msg
+
+			msg.err = sub.Next(&msg.resp)
+			subCh <- msg
+		}()
+
+		var m subMsg
+		// Either can fail, and results in a failed test.
+		//
+		// Using a select prevents us from hanging the test
+		// in the event of a failure and instead reports
+		// back immediately.
+		select {
+		case m = <-subCh:
+		case err := <-postErrCh:
+			require.NoError(t, err, "post 2 messages")
+		}
+		require.NoError(t, m.err, "sub.Next")
+		require.Equal(t, "Hello!", m.resp.MessageAdded.Text)
+		require.Equal(t, "vektah", m.resp.MessageAdded.CreatedBy)
 
-		wg.Wait()
-		var resp interface{}
-		c.MustPost(`mutation { 
-			a:post(text:"Hello!", roomName:"#gophers", username:"vektah") { id } 
-			b:post(text:"Whats up?", roomName:"#gophers", username:"vektah") { id } 
-		}`, &resp)
+		m = <-subCh
+		require.NoError(t, m.err, "sub.Next")
+		require.Equal(t, "Whats up?", m.resp.MessageAdded.Text)
+		require.Equal(t, "vektah", m.resp.MessageAdded.CreatedBy)
 	})
 
 }