Mockito 无法实例化被测类

Question

我有三个类A、B和C:

public class A {
  @Autowired
  private B someB;
  private C someC = someB.getSomeC();
}
@Service
public class B {
  C getSomeC() {
    return new C();
  }
}
public class C { }

现在，如果我为A编写一个单元测试，它看起来像：

@RunWith(MockitoJUnitRunner.class)
public class ATest {
  @InjectMocks
  private A classUnderTest;
  @Mock
  private B someB;
  @Mock
  private C someC;
  @Test
  public void testSomething() {
  }
}

Mockito对此并不满意：

 org.mockito.exceptions.base.MockitoException: 
    Cannot instantiate @InjectMocks field named 'classUnderTest' of type 'class my.package.A'.
    You haven't provided the instance at field declaration so I tried to construct the instance.
    However the constructor or the initialization block threw an exception : null

如果我删除类A中的调用，那么类A看起来如下：

public class A {
  private B someB;
  private C someC;
}

，Mockito能够实例化classUnderTest，并且测试贯穿始终。

为什么会出现这种情况？

编辑：使用Mockito 1.9.5

Answer 1

这是总是会失败：

public class A {
  private B someB;
  private C someC = someB.getSomeC();
}

您正试图对始终为null的值调用getSomeC()。。。将总是抛出CCD_ 8。您需要修复A以更好地处理依赖关系。（就我个人而言，我会将它们作为构造函数参数，但当然还有其他选项…）