Type paramType = getOnlyParameterType();
    TestSubtype spec = method.getAnnotation(TestSubtype.class);
    assertWithMessage("%s is subtype of %s", paramType, returnType)
        .that(TypeToken.of(paramType).isSubtypeOf(returnType))
        .isTrue();
    assertWithMessage("%s is supertype of %s", returnType, paramType)
        .that(TypeToken.of(returnType).isSupertypeOf(paramType))
        .isTrue();
    if (!spec.suppressGetSubtype()) {