@Test
  void resolveTemplateWithHeaderWithJson() {
    String json = "{ \"string\": \"val\", \"string2\": \"this should not be truncated\"}";
    RequestTemplate template =
        new RequestTemplate().method(HttpMethod.GET).header("A-Header", "{aHeader}");

    template = template.resolve(mapOf("aHeader", json));

    assertThat(template).hasHeaders(entry("A-Header", Collections.singletonList(json)));
  }
Avoid depending on guava solely for map literals.
core/src/test/java/feign/RequestTemplateTest.java