I was thinking something along the lines of this (assumes there's a withAction that does a similar thing to withServer but allows you to specify the result that will be returned when a GET request is made):

```scala
"clean up on any onDoneEnumerating callbacks" in {
  val called = new AtomicBoolean()
  withAction(SimpleResult(Enumerator("foo").onDoneEnumerating(called.set()))) {
    await(wsUrl("/get").head())
    called.get() must_== true
  }
}
```