CODEWITHSUNDEEP
javagoogle-cloud-pubsub
dataman
dataman

Reputation: 135

Junit testing a method that returns a callback

I have a callback routine that is used to handle Google pubsub messages:

private MessageReceiver getMessageReceiver() {
    return (message, consumer) -> {
        if (message.getAttributesMap() != null) {
            method1();
        } else {
            method2();
        }
    };
}

I need to write a junit 4 test to verify which method (1 or 2) is invoked, given a message. I know how to do that for a straighforward method, but not a method that returns a callback. can anyone provide a quick example of how to do that?

Upvotes: 0

Views: 316

Answers (1)

Taylor
Taylor

Reputation: 4086

So you've got either a structure or conceptual challenge. I'll put it this way, what's your unit under test?

If it's just the callback, i.e. "when callback is called with such and such message, it should call method1", then method1 needs to become part of your test harness. In other words you need to spy on method1 and method2 so you can capture and assert on when they are and are not called. The challenge here is that the more "clever" you get with spies and mocks, the more complicated and brittle your tests are. You may need to separate getMessageReceiver from the class containing method1 and method2 in this case.

If it's the class containing the getMessageReceiver, method1 and method2 methods, then you need to invoke the callback and assert on the externalities of method1 and method2. E.g. if calling method1 invokes someDelegate.doAThing(), inject a mock of someDelegate and assert that doAThing is called.

Upvotes: 3

Related Questions