I have created a class that runs on the before insert of a custom object.  The purpose is that, if the newly inserted recrod is one of the Integration Users, change the owner to the Agent custom field on the record.
 

public static void UpdateIntegrationOwnerToAgent(List<Productivity_Data__c> data)
    {
        Id profileId = userinfo.getProfileId();
        String ProfileName = [SELECT Name FROM Profile WHERE Id =: profileId LIMIT 1].Name;
        for(Productivity_Data__c d : data)
        {
            system.debug('### ' + d.OwnerId);
            if(ProfileName == 'Integration User')
            {
                system.debug('### Agent: ' + d.Agent__c);
                system.debug('### isActive: ' + d.Agent__r.IsActive);
                if(d.Agent__c != null && d.Agent__r.isActive)
                {
                    d.OwnerId = d.Agent__c;
                } 
            }
        }
    }

As I'm writing my test code, my assertion is failing because the user that I created for the agent field has isActive set to false.  It is my understanding that when you create a user in test methods, they are active.  And this is generally the case, however, my check on the agent__r.IsActive is returning false, therefore not hitting my code that changes the user.
 

public static User getAgent(Boolean xCommit)
    {
        Profile prof = [SELECT Id FROM Profile WHERE Name='AWD Sales'];
        
        User agent = new User();
        agent.Alias = 'standt';
        agent.Email = 'standarduser@testorg.com'; 
        agent.EmailEncodingKey = 'UTF-8';
        agent.LanguageLocaleKey = 'en_US'; 
        agent.LocaleSidKey='en_US';
        agent.TimeZoneSidKey='America/Los_Angeles';
        agent.UserName = 'TestProductivityData@Test.com';
		agent.FirstName = 'Test Agent';
		agent.LastName = 'Integration Test';
		agent.Agent_ID__c = '1234';
        agent.ProfileId = prof.Id;
        
        if(xCommit)
			insert agent;
        return agent;
    }
    
    public static testMethod void Test01TestIntegrationUserChangeToAgent()
    { 
        Profile prof = [SELECT Id FROM Profile WHERE Name = 'Integration User'];
        User intUser = [SELECT Id FROM User WHERE ProfileId =: prof.Id LIMIT 1];
        
        User a = getAgent(true);
        
        List<Productivity_Data__c> pData = generateTestData(5, false);
        
        for(Productivity_Data__c p : pData)
        {
            p.Agent__c = a.Id;
            //p.AgentId__c = a.Agent_ID__c;
            p.OwnerId = intUser.Id;
        }
        Test.startTest();
        system.runAs(intUser)
        {
        	insert pData;
        }
        Test.stopTest();
        
        List<Id> pDataIds = New List<Id>();
        for(Integer i = 0; i < pData.size(); i++)
        {
            pDataIds.add(pData[i].Id);
        }
        
        pData = [SELECT Id, OwnerId, Agent__c FROM Productivity_Data__c WHERE Id IN: pDataIds];
        
        system.assertEquals(a.Id, pData[0].OwnerId);
    }

Yes, I can get around this with adding an if statment to not check isActive when running the tests.  But I would prefer to not do that and have it be tested correctly.  This is coming from a trigger before insert method that takes in the trigger.new list.  Which means, I'm not querying this data, it is coming straight from the trigger, and I would assume.. the relationships should be available in the trigger information.

Thanks