callB.cancel()
          return MockResponse(body = (nextResponse++).toString())
        }
      }
    callA.enqueue(callback)
    callB.enqueue(callback)
    assertThat(server.takeRequest().path).isEqualTo("/a")
    callback.await(requestA.url).assertBody("A")
    // At this point we know the callback is ready, and that it will receive a cancel failure.