MockPostProcessor.java

@Component
public class MockPostProcessor implements BeanPostProcessor {

	/* 
	 * (non-Javadoc)
	 * @see org.springframework.beans.factory.config.BeanPostProcessor#postProcessAfterInitialization(java.lang.Object, java.lang.String)
	 */
	@Override
	public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {

		if (!SimpleUserRepository.class.isInstance(bean)) {
			return bean;
		}

		return Mockito.mock(SimpleUserRepository.class, AdditionalAnswers.delegatesTo(bean));
	}
}

Test.java

public class Test {
  
	@Test
	public void testname() {
		
		// Calls real method
		repository.save(new User());

		// Stubs method call
		when(repository.findAll()).thenReturn(Arrays.asList());

		// Assert on stubbed method
		assertThat(repository.findAll()).isEmpty();

		// Verify method called
		verify(repository).save(any());
		verify(repository).findAll();
	}
}