Mocking method reference as any

Question

I am trying to mock this line:

ResponseEntity<String> response= gatewayOutWrapper.wrap_2P_OneWay(GatewayOut::getConnectionType, wit, serialNumber, metaData);

with when(gatewayOutWrapper.wrap_2P_OneWay(GatewayOut::getConnectionType, any(), any(), any())).thenReturn(ResponseEntity.ok().body(responseBody));

But i dont know how to mock method reference as any. I tried some real values, but i alway get null when run test on that line, so this when dont fire.

Can anyone Help?

Answer 1

Direct answer is that any() should work fine, as Lesiak mentioned in the comments. Java represents method references as implementations of single-method interfaces, and any can mock those interfaces just fine.

You might have found other Mockito pitfalls:

• If you use a matcher like any for any argument when stubbing or verifying, you have to make sure all arguments use matchers. Passing a real value, including your method reference, next to matchers like any() is not allowed. eq is the default, so you can wrap with that.

• If gatewayOutWrapper's class is final, you need to opt-in to final mocking support, or else the null values (that matchers like any() return) will make their way to a real implementation. This is supported in Mockito 2.1+, but it's still not the default behavior as of Mockito 5.

• You might also be getting a null pointer exception if gatewayOutWrapper is a spy or it calls real methods; the solution is to use doReturn as in:

  doReturn(ResponseEntity.ok().body(responseBody))
      .when(gatewayOutWrapper)
      .wrap_2P_OneWay(any(), any(), any(), any());