@Test
public void testDisallowUnknown() throws B2JsonException {

    String json =
            "{\n" +
            "  \"a\": 41,\n" +
            "  \"b\": \"hello\",\n" +
            "  \"x\": 7" +
            "}";
    thrown.expect(B2JsonException.class);
    thrown.expectMessage("unknown field");
    b2Json.fromJson(json, Container.class);
}