PowerMock's expectNew() isn't mocking a constructor as expected

Question

I'm trying to learn the ins and outs of various mocking libraries and PowerMock(specifically the EasyMock extension) is next on the list. I'm attempting to mock a constructor and the examples provided don't have the same response when I try to replicate them. As far as I can tell, it never mocks the constructor and just proceeds as if it were normal.

This is the test class:

@RunWith(PowerMockRunner.class)
@PrepareForTest({Writer.class})
public class FaultInjectionSituationTest {

    @Test
    public void testActionFail() throws Exception {
        FaultInjectionSituation fis = new FaultInjectionSituation();
        PowerMock.expectNew(Writer.class, "test")
           .andThrow(new IOException("thrown from mock"));
        PowerMock.replay(Writer.class);
        System.out.println(fis.action());
        PowerMock.verify(Writer.class);
    }

}

I've tried replacing the "test" with an EasyMock.isA(String.class), but it yielded the same results.

This is the FaultInjectionSituation:

public class FaultInjectionSituation {

    public String action(){
        Writer w;
        try {
            w = new Writer("test");
        } catch (IOException e) {
            System.out.println("thrown: " + e.getMessage());
            return e.getLocalizedMessage();
        }
        return "returned without throw";
    }
}

The "Writer" is nothing more than a shell of a class:

public class Writer {
    public Writer(String s) throws IOException {
    }

    public Writer() throws IOException{
    }
}

When the test is run, it prints out "returned without throw", indicating the exception was never thrown.

rrufai · Accepted Answer · 2013-12-09T14:39:50.137

29

You need to prepare the class that is calling the constructor as well, so PowerMock knows to expect a mocked constructor call. Try updating your code with the following:

@RunWith(PowerMockRunner.class)
@PrepareForTest({Writer.class, FaultInjectionSituation.class})
public class FaultInjectionSituationTest { 
 // as before
}

edited Dec 09 '13 at 14:39

answered Sep 11 '12 at 21:46

rrufai

1,475
14
26

1

Thanks, I did not realize that the object that called the constructor needed to be included as well. – AdamSpurgin Sep 12 '12 at 16:19
I ran into same issue... Precisely what I was missing :) – gp. Jan 13 '14 at 15:16
Thank you very much, I struggled for a long while until I found this answer. – OQJF Jun 18 '15 at 02:02

score 2 · Answer 2 · answered Sep 10 '12 at 23:15

2

You need to first create a mock object:

Writer mockWriter = PowerMock.createMock(Writer.class)
PowerMock.expectNew(Writer.class, "test").andReturn(mockWriter)

answered Sep 10 '12 at 23:15

fo_x86

2,583
1
30
41

I'm not trying to create a mock object, I'm attempting to intercept the constructor and throw an exception in its place. the "more features" section of [this page](http://code.google.com/p/powermock/wiki/MockConstructor) is what I'm aiming for. – AdamSpurgin Sep 10 '12 at 23:26
1

sorry, I see what you are trying to do. I just tried your code on JUnit 4 and it prints out "thrown from mock" (what you'd expect). Are you using TestNG by any chance? I'm not familiar with TestNG but when I ran it using TestNG, I got "returned without throw" – fo_x86 Sep 11 '12 at 03:00
I'm using Junit4. I can't think of anything that would cause it to not work. – AdamSpurgin Sep 11 '12 at 16:04
I don't think there's anything wrong with your code (as I was able to get the desired output). How are you running JUnit? From an IDE or commandline? – fo_x86 Sep 11 '12 at 18:37
I've tried both. I'm handing it to a coworker to run on their machine, maybe that will help illuminate the issue. – AdamSpurgin Sep 11 '12 at 20:38

PowerMock's expectNew() isn't mocking a constructor as expected

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