Thank you so much for your help.

I changed my test code to to query back the opportunities before the assertions..  My basic problem still remains.  The documentation says that on the trigger side of a before insert query, I don't have access to relationship fields, in this case Account.id and Account.name.  This trigger is supposed to copy the custom field information from the related account custom fields.  However, when I build my set of Account IDs in the trigger itself, it is inserting NULL for all of  them and the trigger has no information as to which Account it should be copying from.

Here's the trigger code:

trigger FillFieldsFromAcct on Opportunity (before insert){ 
    set<id> tmpSet = new set<id>();
    for (Opportunity opp : trigger.new){
        tmpSet.add(opp.Account.ID);              //// This is where the NULLs are coming from, because somehow the Account relational fields are disappearing between the Test where they are present, and the Trigger where they are not.
    	system.debug(opp.Account.ID);
    }          
    map<id,Account> acct_map; 
    
    if (!tmpSet.isEmpty()){ 
        acct_map = new map<id,Account>([select id,Mobile__c, Video__c, Display__c, Monthly_Display_Imps__c, Monthly_Mobile_Imps__c, Monthly_Video_Imps__c,
                    uniques__c, vertical__c, Pageviews__c from Account where id in:tmpSet]);
        if(!acct_map.isEmpty())  { 
        for (Opportunity o : trigger.new){
            o.Mobile__c = acct_map.get(o.AccountID).Mobile__c; 
     		o.Video_PubDev__c = acct_map.get(o.AccountID).Video__c;
     		o.Display__c = acct_map.get(o.AccountID).Display__c; 
     		o.Monthly_Display_Impressions__c = acct_map.get(o.AccountID).Monthly_Display_Imps__c; 
     		o.Monthly_Video_Impressions__c = acct_map.get(o.AccountID).Monthly_Video_Imps__c;
         	o.Monthly_Mobile_Impressions__c= acct_map.get(o.AccountID).Monthly_Mobile_Imps__c; 
     		o.Vertical__c = acct_map.get(o.AccountID).Vertical__c; 
     		o.Pageviews__c = acct_map.get(o.AccountID).Pageviews__c;
             o.Uniques__c = acct_map.get(o.AccountID).Uniques__c; 
        }
        }
    } 
}

 Can you suggest any way to solve this problem?  I don't want to use an update trigger because I only want this to happen on insert.  I'm probably doing something wrong in all of this, I know, but can you help me figure out the way to make this work?

for completeness, here's my Test code as it stands:

@isTest
private class TestingOppTrigger {
static testMethod void verify_Opp_Fillin() {
    List<Opportunity> oppsToInsert = new List<Opportunity>();
    List<Account> acctsToInsert = new List<Account>();
    RecordType rt = [select id from RecordType where Name = 'PubDev Opportunities' and SobjectType = 'Opportunity' limit 1];
    integer y = 0;
    Account s = new Account();
    
    Opportunity o = new Opportunity();
        
                        //create Accounts
    
    Account testAcct1 = new Account(Name='KBBTestAcct1', Vertical__c = 'Education',Uniques__c = 30000, Pageviews__c=20000,Display__c=TRUE, Video__c =TRUE,
    Mobile__c = TRUE, Monthly_Display_Imps__c = 500000,Monthly_Mobile_Imps__c = 500003, Monthly_Video_Imps__c = 500002);
    acctsToInsert.add(TestAcct1);
    Account testAcct2 = new Account(Name='KBBTestAcct2');
    acctsToInsert.add(TestAcct2);
    try{
    database.insert(acctsToInsert);
    } catch(DMLException e) {
        system.debug('ERROR:  ' + e);
    }
   	
    //Map inserted Accounts
    string qry3 = 'select name, id, display__c, mobile__c, video__c, Monthly_Display_Imps__c, Monthly_video_Imps__c,' +
        ' Monthly_Mobile_Imps__c, Uniques__c, Pageviews__c, Vertical__c ' + 
           ' from Account where CreatedDate = TODAY'; 
    Map<id, Account> AccountMap = new Map<id, Account>((List<account>)Database.query(qry3));
    
   
    					//Create new Opportunities
     for(y=0;y<2;y++){
            Opportunity TestOppFilled = new Opportunity(RecordTypeID = rt.id, Name='KBBTestOpp' + y, Account= testAcct1, 
            StageName = '3 - On Hold',
            CloseDate = date.parse('3/30/2033'), Pub_Dev_Rep__c = 'Jason');
            oppsToInsert.add(TestOppFilled);
                  
             Opportunity TestOppEmpty = new Opportunity(RecordTypeID = rt.id, Name= 'KBBTestOpp' + 1000 + y,
             Account = testAcct2, StageName = '3 - On Hold',
             CloseDate = date.parse('3/30/2033'), Pub_Dev_Rep__c = 'Jason');
             oppsToInsert.add(TestOppEmpty);
         }
   					// Insert Opportunities
      try{
         system.debug ('trying to insert Opportunities');
         database.insert(oppsToInsert);
         } catch(DMLException e1) {
             system.debug('ERROR:  ' + e1);
         }
    
            List<Opportunity>o_list = new List<Opportunity>();
            o_list = [select display__c, Account.display__c, mobile__c, Account.mobile__c, video__c,Account.video__c,
                                       Monthly_Display_Impressions__c,Account.Monthly_Display_Imps__c, Monthly_video_Impressions__c,
                                       Account.Monthly_Video_Imps__c, Monthly_Mobile_Impressions__c, Account.Monthly_Mobile_Imps__c,
                                       uniques__c, Account.Uniques__c, Pageviews__c, Account.Pageviews__c, Vertical__c, Account.Vertical__c from Opportunity
                                       where name LIKE 'KBBTestOpp%'];
        
                                //verify opportunity copy of account data
            For(Opportunity newOppty : o_list){
                if(newOppty != NULL){
                    if(newOppty.Vertical__c != NULL){
                        system.assertEquals(newOppty.Vertical__c,newOppty.Account.Vertical__c );
                    } else {
                        system.assertEquals(newOppty.Account.Vertical__c, NULL);
                            }
                    
                    if(newOppty.Uniques__c != NULL){
                        system.assertEquals(newOppty.Uniques__c,newOppty.Account.Uniques__c );
                    } else {
                        system.assertEquals(newOppty.Account.Uniques__c, NULL);
                            }
        			if(newOppty.Uniques__c != NULL){
                        system.assertEquals(newOppty.Pageviews__c,newOppty.Account.Pageviews__c );
                    } else {
                        system.assertEquals(newOppty.Account.Uniques__c, NULL);
                            }
         			if(newOppty.Display__c != NULL){
                        system.assertEquals(newOppty.Display__c,newOppty.Account.Display__c );
                    } else {
                        system.assertEquals(newOppty.Account.Display__c, NULL);
                            }
        			if(newOppty.Video_Pubdev__c != NULL){
                        system.assertEquals(newOppty.Video_Pubdev__c,newOppty.Account.Video__c );
                    } else {
                        system.assertEquals(newOppty.Account.Video__c, NULL);
                            }
         			if(newOppty.Mobile__c != NULL){
                        system.assertEquals(newOppty.Mobile__c,newOppty.Account.Mobile__c );
                    } else {
                        system.assertEquals(newOppty.Account.Mobile__c, NULL);
                            }
       				 if(newOppty.Monthly_Display_Impressions__c != NULL){
                        system.assertEquals(newOppty.Monthly_Display_Impressions__c,newOppty.Account.Monthly_Display_Imps__c );
                    } else {
                        system.assertEquals(newOppty.Account.Monthly_Display_Imps__c, NULL);
                            } 
        			if(newOppty.Monthly_Video_Impressions__c != NULL){
                        system.assertEquals(newOppty.Monthly_Video_Impressions__c,newOppty.Account.Monthly_Video_Imps__c );
                    } else {
                        system.assertEquals(newOppty.Account.Monthly_Video_Imps__c, NULL);
                            } 
                                            
         			if(newOppty.Monthly_Mobile_Impressions__c != NULL){
                        system.assertEquals(newOppty.Monthly_Mobile_Impressions__c,newOppty.Account.Monthly_Mobile_Imps__c );
                    } else {
                        system.assertEquals(newOppty.Account.Monthly_Mobile_Imps__c, NULL);
                            } 
                                            }
        
         }
    }
}

I really appreciate all the help you've given me so far.

Kathy