### Question:
MongoPersister extends AbstractPersister<T, StateDocumentImpl> implements
				Persister<T>,
				BeanDefinitionRegistryPostProcessor,
				ApplicationContextAware { @Override protected Field findIdField(Class<?> clazz) { Field idField = getReferencedField(this.getClazz(), Id.class); if (idField == null) { idField = getReferencedField(this.getClazz(), javax.persistence.Id.class); if (idField == null) { idField = getReferencedField(this.getClazz(), EmbeddedId.class); } } return idField; } MongoPersister(
			List<State<T>> states,
			State<T> startState,
			Class<T> clazz,
			MongoTemplate mongoTemplate);  MongoPersister(
			List<State<T>> states,
			String stateFieldName,
			State<T> startState,
			Class<T> clazz,
			MongoTemplate mongoTemplate);  MongoPersister(
			List<State<T>> states,
			State<T> startState,
			Class<T> clazz,
			String repoId);  MongoPersister(
			List<State<T>> states,
			String stateFieldName,
			State<T> startState,
			Class<T> clazz,
			String repoId); @Override void setApplicationContext(ApplicationContext applicationContext); @Override void setCurrent(T stateful, State<T> current, State<T> next); @Override void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory); @Override void postProcessBeanDefinitionRegistry(
			BeanDefinitionRegistry registry);  }### Answer:
@Test public void testJPAId() throws StaleStateException { Field field = this.jpaIdPersister.findIdField(JPAIdEntity.class); assertNotNull(field); }