How to mock An Interface Java PowerMockito

Question

I m trying to mock an interface.

public interface FlowCopyParamsBusinessManager {
List<FlowCopyParams> findByAppli(String application, String sourcePattern)
        throws FlowCopyParamsBusinessException;

}

In my code, when i call this method findByAppli, i would like to return a list of FlowCopyParams.

List<FlowCopyParams> lstFlowCopyParams = flowCopyParamsBusinessManager.findByAppli(
                    "TOTO","TATA);

Here my try in the class test:

@BeforeClass
public static void mockBeanIn() throws Exception {
List<FlowCopyParams> flowCopyParamsList = new ArrayList<>();

PowerMockito.spy(FlowCopyParamsBusinessManager.class);
PowerMockito.when(FlowCopyParamsBusinessManager.class, "findByAppli",  Mockito.anyString(), Mockito.anyString()).thenReturn(flowCopyParamsList);
}  

I have this error :

java.lang.IllegalArgumentException: object is not an instance of declaring class

I don't know why because the method findByAppli must have two string parameters, and i put Mockito.anyString() and i still have IllegalArgumentException.

Any clue ?

Thxs.

Answer 1

You don't need to use PowerMockito, and as its an Interface, theres no need to spy() as you are not relying on any non mocked logic.

It can be done like this, in your test class define a class variable.

private FlowCopyParamsBusinessManager flowCopyParamsBusinessManagerMock;

In an @Before annotated method:

flowCopyParamsBusinessManagerMock = Mockito.mock(FlowCopyParamsBusinessManager.class);
List<FlowCopyParams> flowCopyParamsList = new ArrayList<>();
when(flowCopyParamsBusinessManagerMock 
.findByAppli(Mockito.anyString(), Mockito.anyString()).thenReturn(flowCopyParamsList);

Then refer to flowCopyParamsBusinessManagerMock in your tests.

Answer 2

My test did not work because I was trying to spy the class and not on the instance of FlowCopyParamsBusinessManager.class .

First , we have to create the mock :

FlowCopyParamsBusinessManager mockFlowCopyParamsBusinessManager = PowerMockito.mock(FlowCopyParamsBusinessManager.class);

Then , spy the instance :

PowerMockito.spy(mockFlowCopyParamsBusinessManager);
PowerMockito.when(mockFlowCopyParamsBusinessManager, "findByAppli", Mockito.anyString(), Mockito.anyString()).thenReturn(flowCopyParamsList);

It works as well !