Testing static java methods with arguments as functions

Question

I'd like to write a test for verification if static method receiving correct callable as an argument. Let's say I have 2 classes:

Employee

public class Employee {
    public static Item getEmployeeItem() {
        return new Item((a, b) -> {
            return a * b;
        });
    }
}

and Item

public class Item {
    BiFunction<Integer, Integer, Integer> behaviour;
    Item(BiFunction<Integer, Integer, Integer> biFunction) {
        this.behaviour = biFunction;
    }

}

Item has constructor with BiFunction. I'd like to to test with using junit5, Mockito, PowerMock or maybe other utills, behaviour when in case when I call

Item item = Employee.getEmployeeItem();

then appriopriate BiFunction has been delivered. How can I write such kind of test with junit5? Maybe should I use somehow ArgumentCaptor? Can someone deliver me example?

That's actually simpler example of more advanced case which I need to test in unit way in my job:

@NoArgsConstructor(access = AccessLevel.PRIVATE)
public class EthernetExtractFilterFrameParsingNodeDefinitions {

    public static ExtractFilterTreeNodeDefinition<EthernetExtractFilter, EthernetDataTuple, IpProtocol, Option<Vector<SingleDataSet>>> getIpProtocolNodeDefinition() {
        return new ExtractFilterTreeNodeDefinition<>(
                ethernetExtractFilter -> ethernetExtractFilter.networkLayerPduFilter().ipProtocolFilter().toValueFilter(),
                getNodeBehaviour(ethernetDataTuple -> ethernetDataTuple.networkLayerPdu().getIpProtocol())
        );
    }

}

I have to check here if ExtractFilterTreeNodeDefinition was created with appropriate Functions as parameters when I call getIpProtocolNodeDefinition() statick method.

I'd like to be sure that first argument is correct function, correctly map extractFilter to valueFilter:

ethernetExtractFilter -> ethernetExtractFilter.networkLayerPduFilter().ipProtocolFilter().toValueFilter()

second one as well How to approach to that problem? I would be grateful for suggestions how to achieve that.