if (priorResponse != null && priorResponse.code == HTTP_CLIENT_TIMEOUT) {
          // We attempted to retry and got another timeout. Give up.
          return null
        }

        if (retryAfter(userResponse, 0) > 0) {
          return null
        }

        return userResponse.request
      }

      HTTP_UNAVAILABLE -> {
        val priorResponse = userResponse.priorResponse

        response.getWriter()
                .write("{\"response\":{\"status\":9,\"message\":\"Server is busy. Please retry after " + RETRY_AFTER_SECONDS
                        + " seconds.\",\"retry_after\":" + RETRY_AFTER_SECONDS + "}}");
    }

        assertEquals("60", mockResponse.getHeaderValue("Retry-After"));
        assertTrue(mockResponse.getWriterOutput().contains("\"status\":9"));
        assertTrue(mockResponse.getWriterOutput().contains("\"retry_after\":60"));
    }

    @Test
    public void test_doFilter_apiAtThreshold() throws IOException, ServletException {
        setConfig(100, 80);
        testableFilter.setCpuPercent((short) 80);

   *
   * @since 27.1
   */
  public static final String REPORT_TO = "Report-To";

  /** The HTTP {@code Retry-After} header field name. */
  public static final String RETRY_AFTER = "Retry-After";

  /** The HTTP {@code Server} header field name. */
  public static final String SERVER = "Server";

  /**