@Test
  void resolveTemplateWithHeaderContainingJsonLiteral() {
    String json = "{\"A\":{\"B\":\"C\"}}";
    RequestTemplate template =
        new RequestTemplate().method(HttpMethod.GET).header("A-Header", json);

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