Mockito when/thenReturn always returning null in Scala Test when trying to mock rabbitmq ConnectionFactory

1
votes

I'm trying to mock the RabbitMQ ConnectionFactory object to return a mocked connection, using scalatest and mockito. Below is an example test that I am using:

class RabbitMQMockTest extends FunSuite with MockitoSugar {
    test("RabbitMQ ConnectionFactory is correctly mocked") {
        def connectionFactory = mock[ConnectionFactory]
        def connection = mock[Connection]

        when(connectionFactory.newConnection()).thenReturn(connection)
        println(connectionFactory.newConnection())

        assert(connectionFactory.newConnection() != null)
    }
}

This always fails and the println statement always prints "null". I am very new to using these technologies together and was wondering if anyone had any advice or could let me know if I'm doing anything wrong. Thanks in advance!

2
scalarabbitmqmockitoscalatest
Can you break up your test to only rely on the mock Connection? It's generally nasty to mock multiple levels of dependencies this way -- you'll end up maintaining lots of fragile mock code which itself doesn't add value to your project. – earldouglas
Yeah, I agree having a mock that returns a mock is usually a test smell. For something near the connecting stuff I would instead write integration tests rather than unit tests. About your issue, do you have the same erratic behavior with other classes (like your classes). – Brice
Hey guys, thanks for the responses! I definitely agree with you both, that this is far from ideal, and I plan on refactoring the class under test to allow for better dependency injection. I did however solve my problem, and it turns out I made a bone headed mistake. I defined the mock classes using 'def' instead of 'val' or 'var', so it turns out I was creating a new mock every time I called one of the methods. Sorry to waste you guys' time, thanks again for the comments! – Bryan

2 Answers

5
votes

Don't accidentally define variables using 'def'! I defined the mocks using 'def' instead of 'val' or 'var', so I created a method that returns a new mock every time, instead of a variable.

0
votes

I think you should define a behavior on connection mock before being able to use it. For example :

when(connection.createChannel()).thenReturn(new Channel {...})

or something like this.