@Test
  void resolveTemplateWithHeaderSubstitutions() {
    RequestTemplate template =
        new RequestTemplate().method(HttpMethod.GET).header("Auth-Token", "{authToken}");

    template = template.resolve(mapOf("authToken", "1234"));

    assertThat(template).hasHeaders(entry("Auth-Token", Collections.singletonList("1234")));
  }
Avoid depending on guava solely for map literals.
core/src/test/java/feign/RequestTemplateTest.java