Hello 
I cant solve this, maybe someone can help me

System.DmlException: Update failed. First exception on row 0 with id 0066E000004pfWbQAI; first error: FIELD_CUSTOM_VALIDATION_EXCEPTION, In the stage Demo, you need to fill in the fields "Scope Test Determined", Testperiod In Salesforce" and Order Task Sent to Salesforce".: []

static testMethod void testClosedWonUpdate_positive_03(){
List<Opportunity> oppList = [SELECT Id, StageName,End_Date_Test_Phase__c FROM Opportunity WHERE Name LIKE 'Test%' LIMIT 1];
Opportunity opp = oppList.get(0);
opp.StageName = 'Test';
Date d = date.today();
opp.End_Date_Test_Phase__c = d.addDays(40);
update opp;
System.debug(' 632 ====> ' + opp);
List<Account> aList = [SELECT Id, Name FROM Account WHERE Name LIKE 'Test%' LIMIT 1];
Account a = aList.get(0);
System.debug(' 636 ====> ' + a);
List<Asset> assets = [SELECT Id, Price_Agreements__c, Price, Status, Product2Id, Test_Asset__c, IsCompetitorProduct
FROM Asset WHERE AccountId = :a.Id];
System.debug(' 640 ====> ' + assets);
System.assertEquals('In test', assets[0].Status);
Test.startTest();
opp.StageName = 'Closed Won';
update opp;
Test.stopTest();
OpportunityLineItem ol = [SELECT OpportunityId FROM OpportunityLineItem WHERE Name LIKE 'Test%'];
List<Asset> assets1 = [SELECT Id, Price_Agreements__c, Price, Product2Id, Test_Asset__c, IsCompetitorProduct
FROM Asset WHERE AccountId = :a.Id];
List<OpportunityLineItem> oliList = [select Id, Asset__c from OpportunityLineItem where Id =: ol.Id LIMIT 1];
System.assertEquals(1, assets1.size());
System.debug(' 657 ====> ' + assets1);
System.assertEquals(false, assets1[0].Test_Asset__c);
System.assertEquals(false, assets1[0].IsCompetitorProduct);
System.assertEquals(oliList[0].Asset__c, assets1[0].Id);
}

Let me know