public <T> T entity(Class<T> entityClass) {
        try {
            return mapper.reader(entityClass).readValue(body);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
@param entityClass the entity class
@return the body as an entity (JSON marshalling)
test/policies/src/main/java/io/apiman/test/policies/PolicyTestResponse.java