PowerMockito.mockStatic() but still getting NPE when static method is called

Question

NOTE - I've marked 3 LINE numbers which I discuss in my question, you may need to scroll to the right in the code snippets to see.

I'm really struggling unit testing a method with chained Optional.map()s.

@Override
public void accept(Object message)
{
    extractSenderReference(message.toString())
        .map(t ->
        {
            t.setTransactionStatus("TAG1"); //  <- LINE #1
            return t;
        })
        .map(StaticConverter::convert) //< -LINE #2
        .ifPresent(Persist::persist);
}

Where extractSenderReference() returns an Optional of type Obj and is a private method.

And my test:

@RunWith(PowerMockRunner.class)
@PrepareForTest({ClassBeingTested.class, StaticConverter.class})

public class MyTest {

private ClassBeingTested updateProcessor = PowerMockito.spy(new ClassBeingTested());
private StatusDataObj statusDataObj = mock(StatusDataObj.class);

@Test
public void testSomething() throws Exception{
    Obj myObj = getObj();
    PowerMockito.mockStatic(StaticConverter.class);

    PowerMockito.doReturn(Optional.ofNullable(myObj)).when(updateProcessor, "extractSenderReference", anyString()); // <- LINE #3
    when(StaticConverter.convert(myObj)).thenReturn(statusDataObj);
    updateProcessor.accept("MESSAGE1");
}

private Obj getObj(){
    Obj obj = new Obj();
    obj.setId(100L);
    return obj;
 }
}

At LINE #1, as marked in my accept() method, object t has been processed and has had its transactionStatus set successfully. However at LINE #2 I am getting a NPE when running the above test.

I've also tried PowerMockito.spy(StaticConverter.class); instead of PowerMockito.mockStatic(StaticConverter.class); as per https://github.com/powermock/powermock/wiki/Mockito#mocking-static-method but I'm getting the same NPE.

My thinking was map is converting t to StatusDataObj type. So when map calls convert, I'll stub and return my type. However, originally I was expecting that LINE #3 would effectively take care of the chained map calls on the Optional returned from extractSenderReference(), since I'm using a real object with values set, but there must be a null value somewhere else?

Could your code by any chance be presented as [a Minimal, Complete, and Verifiable example](https://stackoverflow.com/help/mcve), please? When I try to read through it, I feel there are quite many unknowns. — Ole V.V., Jan 29 '19 at 14:01
Does `Obj` implement `equals` (and `hashCode`) correctly? If not, I suspect it might stand a better chance of working if you store `getObj()` in a variable, and use it in both places. — Andy Turner, Jan 29 '19 at 14:03
@AndyTurner good shout but unfortunately the same outcome. I've updated the snippets to reflect the change. — notAChance, Jan 29 '19 at 14:11
@OleV.V. I've removed some method calls and replaced with return types to simplify. — notAChance, Jan 29 '19 at 14:14
@MaciejKowalski Updated. I have included `@PrepareForTest({ClassBeingTested.class, StaticConverter.class})` in my code, if this is what you're after :) — notAChance, Jan 29 '19 at 14:33
Try replacing the method reference `StaticConverter::convert` with an explicit lambda call to the actual method: `e -> StaticConverter.convert(e)`. — nickb, Jan 30 '19 at 15:14

score 1 · Answer 1 · answered Jan 30 '19 at 15:27

Try replacing the method reference StaticConverter::convert with an explicit lambda call to the actual method: e -> StaticConverter.convert(e).

I've had issues with Powermock mocking method references, but by leaving it as an explicit method call I could successfully mock those calls.

score 0 · Answer 2 · answered Jan 29 '19 at 14:34

0

You need to add the classes to the @PrepareForTest with which you will be working in that test:

@RunWith(PowerMockRunner.class)
@PrepareForTest(StaticConverter.class, ClassBeingTested.class)

Powermock needs to be aware you will be using it for these classes.

answered Jan 29 '19 at 14:34

Maciej Kowalski

25,605
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These are included, I've updated my code example. Getting same `NPE` – notAChance Jan 29 '19 at 14:35
are you sure the first map does not transform to an Optional? Also ifPresent is part of an Optional inerface, not Stream. Also that stream has no terminal operation, how does that even compile /run? – Maciej Kowalski Jan 29 '19 at 14:42
The first map does transform to an `Optional`. – notAChance Jan 29 '19 at 14:45
is StaticConverter.convert overloaded? – Maciej Kowalski Jan 29 '19 at 14:55
Nope, there's only one method in the `StaticConverter` class, and it's called `convert`. – notAChance Jan 29 '19 at 14:58

score 0 · Accepted Answer · answered Jan 30 '19 at 22:25

0

Persist was null. I'm not sure why the NPE was at LINE 2.

answered Jan 30 '19 at 22:25

notAChance

1,360
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PowerMockito.mockStatic() but still getting NPE when static method is called

3 Answers3