Platform Event Trigger Test: Set CreatedById OR catch trigger exceptions?

Question

I have a Platform Event with a trigger I am writing tests for. This trigger inserts a record and throws a custom exception if there is a DML error. I want to make assertions about the message in that exception.

If I use EventBus.publish() and Test.stopTest(), the exception won't be thrown inside the test, since the trigger executes in a separate transaction. So instead, I have my trigger logic in an Apex class, which I can test directly.

So far so good, but here's the wrinkle: my trigger logic sets the OwnerId of the record I'm creating based on the CreatedById in the Platform Event. And Apex doesn't allow you to set CreatedById on the event record directly -- you have to actually create the record. Which is fine if you're using a regular custom object -- you can query that type of info. But Platform Events aren't queryable.

So now I'm getting a DML error, INVALID_CROSS_REFERENCE_KEY: Owner ID: owner cannot be blank -- but that isn't the DML error I'm trying to test for.

Is there anything I can do to set the CreatedById on the event? Or alternatively, is there any way to catch exceptions that come from a Platform Event trigger execution?

Answer 1

You can fabricate a platform event using something like:

String theUserId = ...;

Map<String, Object> eventMap = new Map<String, Object> {
        'attributes' => new Map<String, Object> {
                'type' => 'MyEvent__e'
        },
        'MyField__c' => 'Xyz',
        'CreatedById' => theUserId
};

MyEvent__e fabricated = (MyEvent__e) JSON.deserialize(JSON.serialize(eventMap), MyEvent__e.class);

This deserialization approach allows you to fake out not just your custom fields but also the system fields as well, as shown above with the CreatedById. You can use this for platform events and ordinary SObjects too.

You can then pass this event into your apex trigger handler code as required.