@isTest
public class PlatformEventTest {
    @isTest static void test1() {
        // Create test event instance
        Order_Event__e newsEvent = new Order_Event__e(
             Has_Shipped__c = true);

       Test.startTest();

        // Call method to publish events
        Database.SaveResult sr = EventBus.publish(newsEvent);

        Test.stopTest();

        // Perform validation here
        // Check that the task that the trigger created is present.
        List<Task> tasks = [SELECT Id FROM Task];
        // Validate that this task was found.
        // There is only one test task in test context.
        System.assertEquals(1, tasks.size());
    }
}

// Trigger for listening to Order events.

trigger OrderEventTrigger on Order_Event__e (after insert) {

            // List to hold all tasks to be created.

   List<Task> tasks = new List<Task>();

            // Iterate through each notification.

    for (Order_Event__e event : Trigger.New) {
        if (event.Has_Shipped__c == true) {

            // Create task for team to follow up on the shipped order.

      Task tk = new Task();
            tk.Priority = 'Medium';
            tk.Status = 'New';
            tk.Subject = 'Follow up on shipped order to ' +
                event.Order_Number__c;
            tk.OwnerId = UserInfo.getUserId();
            tasks.add(tk);
        }

            // Insert all tasks corresponding to events received.
    insert tasks;
    }
}