i have written a test class where i am comparing 2 fields. One of that fields is related to a formula field in an opportunity. More in detail: One field in the opportunity is filled by formula with a value from the linked account. This field is called 'Source_Details__c' in both, opp and acc. Another field in the opportunity will be filled with a trigger, based on that formula field. When i run a test class, i need to have the formula field to be filled, but it seems, that field is not filled, does a testclass not run formula fields? Maybe i should add the error message here:

System.SObjectException: SObject row was retrieved via SOQL without querying the requested field: Opportunity.Source_Details__c

and here is the test class

@IsTest
public class TestClassOppCaseStore {
static testMethod void TestClassOppCaseStore_trigger(){
Account a = new Account(Name = 'testAccount',
                        BillingPostalCode = '83059',
                       BillingCountry = 'Deutschland',
                       Source_Details__c = 'Düren (Saturn)');
insert a; 
Lead l = new Lead (LastName = 'Musterhausen',
                   Country = 'Deutschland',
                   Company = 'MeierEisen',
                   PostalCode = '12457',
                   LeadSource = 'Import',
                   Status = 'new');
insert l;

Event k = new Event (Subject = 'Testing',
                     WhoId = l.Id,
                     StartDateTime = date.today(),
                    EndDateTime = date.today());
    insert k;

Event m = new Event (Subject = 'Testing',
                     WhatId = a.Id,
                     StartDateTime = date.today(),
                    EndDateTime = date.today());
    insert m;

Task t = new Task (Subject = 'Demotermin',
                   WhatId = a.Id);
 insert t;

Task u = new Task (Subject = 'Demotermin',
                   WhoId = l.Id);
 insert u;

    Pricebook2 d = new Pricebook2 (Name = 'Standard');
insert d;
Product2 e =new Product2 (Name = 'Top AG',
                          VK_netto__c = 12);
insert e;
        Opportunity g = new Opportunity (Name = 'testOpp',
                                  AccountId = a.Id,
                                 Amount = 250,
                                 StageName = 'new',
                                 CloseDate = date.today(),
                                 related_Partner_Supplier__c = a.Id);
    insert g;
    update a;
    update g;
CKSW_BASE__Service__c serv = new CKSW_BASE__Service__c (Opportunity__c = g.Id,
                                                       CKSW_BASE__Account__c = a.Id,
                                                       CKSW_BASE__Status__c = 'new');
insert serv;
Case c = new Case (Subject = g.Name,
                  AccountId = a.Id,
                  related_Partner_Supplier__c = a.Id);
insert c;
g = [SELECT Account.Id, Source_Details__c FROM Opportunity WHERE Id = :g.Id];
System.AssertEquals(a.Id, g.AccountID);
Account ag = [SELECT Id FROM Account WHERE Name = :g.Source_Details__c];
System.AssertEquals(ag.Id, g.related_Partner_Supplier__c);
c = [SELECT Account.Id, Account_Source_Details__c FROM Case WHERE Id = :c.Id];
System.AssertEquals(a.Id, c.AccountID);
Account ac = [SELECT Id FROM Account WHERE Name = :c.Account_Source_Details__c];
System.AssertEquals(ac.Id, c.related_Partner_Supplier__c);}}