/**
     * Returns the names of the request headers that need to be checked for equality when caching.
     */
    private fun Headers.varyFields(): Set<String> {
      var result: MutableSet<String>? = null
      for (i in 0 until size) {
        if (!"Vary".equals(name(i), ignoreCase = true)) {
          continue
        }

        val value = value(i)
        if (result == null) {

    val cloned = call.clone()
    cloned.enqueue(callback)
    val firstResponse = callback.await(request.url).assertSuccessful()
    val secondResponse = callback.await(request.url).assertSuccessful()
    val bodies: MutableSet<String?> = LinkedHashSet()
    bodies.add(firstResponse.body)
    bodies.add(secondResponse.body)
    assertThat(bodies).contains("abc")
    assertThat(bodies).contains("def")
  }

  @Test