java - PowerMockito 在尝试 stub 私有(private)重载方法时抛出 NullPointerException

Question

我(仍然)尝试使用 PowerMockito 检查 bar(Alpha, Baz) 是否调用 bar(Xray, Baz) (如 bar(Xray) , Baz) 是 private) - 没有实际调用后者，因为我的 MCVE 类 Foo 下面。 (我经历了同一个类 earlier ，Foo 中的所有方法都是 public - 如果您有似曾相识的感觉...)

public class Foo {
    private String bar(Xray xray, Baz baz) {
        return "Xray";
    }

    private String bar(Zulu zulu, Baz baz) {
        return "Zulu";
    }

    public String bar(Alpha alpha, Baz baz) {
        if(alpha.get() instanceof Xray) {
            return bar((Xray)alpha.get(), baz);
        } else if(alpha.get() instanceof Zulu) {
            return bar((Zulu)alpha.get(), baz);
        } else {
            return null;
        }
    }
}

当我尝试运行下面的测试时，我从 PowerMock 得到一个 NPE:

@RunWith(PowerMockRunner.class)
// @PrepareOnlyThisForTest(Foo.class) // we aren't looking at the byte code, I think
public class FooTest {

    @Test
    public void testBar_callsBarWithXray() throws Exception {
        Baz baz = new Baz(); //POJOs
        Alpha alpha = new Alpha();
        alpha.set(new Xray());

        Foo foo = new Foo();
        Foo stub = spy(foo); // using Mockito, as it's neither final nor "not spyable"

        // NPE at org.powermock.api.mockito.internal.expectation.PowerMockitoStubberImpl.addAnswersForStubbing(PowerMockitoStubberImpl.java:67)
        PowerMockito.doReturn("ok").when(stub, "bar", Xray.class, Baz.class);

        stub.bar(alpha, baz);
        // Testing if bar(Xray, Baz) was called by bar(Alpha, Baz)
        PowerMockito.verifyPrivate(foo).invoke("bar", Xray.class, Baz.class);
        // Mockito's equivalent for a public method: verify(stub, times(1)).bar(any(Xray.class), any(Baz.class));
    }
}

如果我将 stub 设置为 PowerMockito.spy(foo)，我会收到 IllegalArgumentException: argument type mismatch at org.powermock.reflect.internal.WhiteboxImpl.performMethodInitation(WhiteboxImpl.java :2014) 相反。 (它与 NPE 在同一行冒泡。)

我正在使用 Mockito-core 1.9.5、PowerMock 1.5.4(module-junit4 和 api-mockito)和 JUnit 4.11。

我需要更改什么才能阻止抛出异常？我怎样才能让这个测试发挥作用？ (除了 testing that 我的类(class)工作，而不是如何...;-))

Answer 1

在设置期望时，我们必须使用精确的参数匹配器。在你的情况下，它是 Matchers.any(Xray.class)、Matchers.any(Baz.class)

我已按如下方式修改了您的代码，并在测试方法的输出对象上添加了断言语句。

@RunWith(PowerMockRunner.class)
//@PrepareOnlyThisForTest(Foo.class) // we aren't looking at the byte code, I think
 public class FooTest {

   @Test
   public void testBar_callsBarWithXray() throws Exception {
       Baz baz = new Baz(); //POJOs
       Alpha alpha = new Alpha();
       alpha.set(new Xray());

       Foo foo = new Foo();
       Foo stub = PowerMockito.spy(foo); // using Mockito, as it's neither final nor "not spyable"

      // NPE at org.powermock.api.mockito.internal.expectation.PowerMockitoStubberImpl.addAnswersForStubbing(PowerMockitoStubberImpl.java:67)
      PowerMockito.doReturn("ok").when(stub, "bar", Matchers.any(Xray.class), Matchers.any(Baz.class));

      String res = stub.bar(alpha, baz);
      Assert.assertEquals("ok", res);

     //Testing if bar(Xray, Baz) was called by bar(Alpha, Baz)
     PowerMockito.verifyPrivate(stub).invoke("bar", Matchers.any(Xray.class), Matchers.any(Baz.class));
     // Mockito's equivalent for a public method: verify(stub, times(1)).bar(any(Xray.class), any(Baz.class));
   }
}

观察:当调用验证方法时，我们必须传递 stub 对象而不是实际对象，因为我们对 stub 对象设置了期望。由于我添加了断言语句来测试该方法，因此您不必在 stub 上验证它是否正常工作。

添加: 我在公共(public)和私有(private)“bar”方法中添加了 sysout 语句，当我再次测试时，我发现公共(public) bar 方法的 sysout 语句没有打印。 这意味着上面的代码只模拟了公共(public)方法，而没有模拟私有(private)方法。

为了模拟私有(private)“bar”方法，我尝试使用 MemberMatcher.method 进行另一种模拟，效果非常好。

import org.powermock.api.support.membermodification.MemberMatcher;

@RunWith(PowerMockRunner.class)
@PrepareForTest(Foo.class) // we need this
public class FooTest {

@Test
 public void testBar_callsBarWithXray() throws Exception {
     Baz baz = new Baz(); //POJOs
     Alpha alpha = new Alpha();
     alpha.set(new Xray());

     Foo stub = PowerMockito.spy(new Foo());

     PowerMockito.doReturn("ok")
        .when(stub,
                MemberMatcher.method(Foo.class,
                        "bar",
                        Xray.class, Baz.class))
        .withArguments(Matchers.any(Xray.class), Matchers.any(Baz.class));

     String res = stub.bar(alpha, baz);

     Assert.assertEquals("ok", res);

     //Testing if bar(Xray, Baz) was called by bar(Alpha, Baz)
     PowerMockito.verifyPrivate(stub).invoke("bar", Matchers.any(Xray.class), Matchers.any(Baz.class));
     // Mockito's equivalent for a public method: verify(stub, times(1)).bar(any(Xray.class), any(Baz.class));
 }

 output : public bar

测试方法也通过了。下面是具有 sysouts 的 foo 方法。

private String bar(Xray xray, Baz baz) {
    System.out.println("private bar");
    return "Xray";
}

public String bar(Alpha alpha, Baz baz) {

    System.out.println("public bar");

    if(alpha.get() instanceof Xray) {
        return bar((Xray)alpha.get(), baz);
    } else if(alpha.get() instanceof Zulu) {
        return bar((Zulu)alpha.get(), baz);
    } else {
        return null;
    }
}