MaxAgeTest.java

  @Test public void foo() throws Exception {
    server.enqueue(new MockResponse()
        .addHeader("Cache-Control: max-age=7200")
        .addHeader("Connection: Keep-Alive")
        .addHeader("Content-Type: text/html")
        .addHeader("Date: " + formatDate(-5, TimeUnit.SECONDS))
        .addHeader("Keep-Alive: timeout=3, max=100")
        .addHeader("Server: Apache/2.2.26 (Unix)")
        .addHeader("X-Powered-By: PHP/5.3.28")
        .setChunkedBody("A", 1024));
    server.enqueue(new MockResponse()
        .setBody("B"));
    server.play();

    URL url = server.getUrl("/");
    HttpURLConnection c1 = openConnection(url);
    assertEquals("A", readAscii(c1));
    System.out.println(c1.getHeaderField("OkHttp-Response-Source"));

    HttpURLConnection c2 = openConnection(url);
    assertEquals("A", readAscii(c2));
    System.out.println(c2.getHeaderField("OkHttp-Response-Source"));
  }

You can run this yourself by pasting it into OkHttp's ResponseCacheTest.java. It prints the following:

NETWORK 200
CACHE 200