languageHelper.updateDocument(doc);

        assertEquals("ja", doc.get("lang"));
        assertEquals("タイトル", doc.get("title_ja"));
        assertEquals(123, doc.get("content_ja"));
        assertNull(doc.get("url_ja")); // url is not in langFields
    }

    @Test
    public void test_updateDocument_withNullLangFields() {
        Map<String, Object> doc = new HashMap<>();
        doc.put("lang", "ja");

  fun iterateCache() {
    // Put some responses in the cache.
    server.enqueue(
      MockResponse
        .Builder()
        .body("a")
        .build(),
    )
    val urlA = server.url("/a")
    assertThat(get(urlA).body.string()).isEqualTo("a")
    server.enqueue(
      MockResponse
        .Builder()
        .body("b")
        .build(),
    )
    val urlB = server.url("/b")