tests: Replace counter increment with channel to avoid data race

Author: rhansen

internal/generator/generator_test.go

@@ -22,7 +22,10 @@ import (
 func TestGenerateFromEvents(t *testing.T) {
 	log.SetOutput(ioutil.Discard)
 	containerID := "8dfafdbc3a40"
-	counter := 0
+	counterCh := make(chan int, 50)
+	for i := 1; len(counterCh) < cap(counterCh); i++ {
+		counterCh <- i
+	}
 
 	eventsResponse := `
 {"status":"start","id":"8dfafdbc3a40","from":"base:latest","time":1374067924}
@@ -67,7 +70,7 @@ func TestGenerateFromEvents(t *testing.T) {
 		json.NewEncoder(w).Encode(result)
 	}))
 	server.CustomHandler(fmt.Sprintf("/containers/%s/json", containerID), http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		counter++
+		counter := <-counterCh
 		container := docker.Container{
 			Name:    "docker-gen-test",
 			ID:      containerID,