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.

> here is the formula: "text( Account.Source_Details__c )" the field in
> Opportunity is called same 'Source_Details__c'

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.QueryException: List has no rows for assignment to SObject
 
here is the trigger`trigger update_related_Supplier on Opportunity (before insert, before update) {
    
    for (Opportunity opp: Trigger.new) {
         if(opp.Source_Details__c != null){
               Account[] acc = [Select Id from Account where Name = :opp.Source_Details__c] ;
             if(acc.size() > 0){
                 opp.related_Partner_Supplier__c = acc[0].Id;}
             else  {            opp.related_Partner_Supplier__c = null;
             }}}}`




   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);}}