单元测试DEMO

import lombok.extern.slf4j.Slf4j;
import org.junit.Before;
import org.junit.Test;
import org.mockito.Mockito;

import java.lang.reflect.Field;
import java.util.Optional;

@Slf4j
public class AppServiceImplTest {
  private AppServiceImpl appService = new AppServiceImpl();

  private AppDao appDao;

  @Before
  public void initAppService() {
    try {
      appDao = Mockito.mock(AppDao.class);
      Field field = appService.getClass().getDeclaredField("appDao");
      field.setAccessible(true);
      field.set(appService, appDao);
    } catch (NoSuchFieldException | IllegalAccessException e) {
      log.error("initAppService failed", e);
    }
  }

  @Test
  public void testFindById_Normal() {
    Mockito.doReturn(Optional.of(new App())).when(appDao).findById(1L);
    assert appService.findById(1L) != null;
  }

  @Test
  public void testFindById_Null() {
    Mockito.doReturn(Optional.empty()).when(appDao).findById(null);
    assert appService.findById(null) == null;
  }

  @Test
  public void testFindById_NotExists() {
    Mockito.doReturn(Optional.empty()).when(appDao).findById(Long.MAX_VALUE);
    assert appService.findById(Long.MAX_VALUE) == null;
  }

}