Apex Class:
public with sharing class ChangeOpptyOwnerCtrl {
    private string oppId;
    public Opportunity oppobj {get;set;}
    public boolean isErrInSave {get;set;}
    
    public ChangeOpptyOwnerCtrl(ApexPages.StandardController ctrl){
        oppId = ApexPages.currentPage().getParameters().get('oppId');
        if(oppId != null)
            oppobj = [Select id, Name, OwnerId from Opportunity where id =: oppId limit 1];
    }
    
    public void saveOwner(){
        isErrInSave = false;
        try{
            if(oppobj != null)
                update oppobj;
        }catch(Exception e){
            ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.Error , e.getMessage()));
            isErrInSave = true;
        }
    }
}


TestClass:

@isTest
public with sharing class ChangeOpptyOwnerCtrlTest {
    @testSetup
    static void setupTestData(){
        Account acc = TestUtility.createAccount('Test A');
        insert acc;
        Opportunity opp = TestUtility.createOpportunity('@test opp', Date.today(), 'To be Invoiced', acc.id);
        opp.Follow_up_Date__c = date.today();
        insert opp;
    }
    
    testmethod static void saveOwnerTest(){
        Opportunity opp = [Select id from Opportunity limit 1];
        test.startTest();
        
        Test.setCurrentPageReference(new PageReference('Page.ChangeOpptyOwnerPage'));
        System.currentPageReference().getParameters().put('oppId',opp.id);        
        ApexPages.StandardController sc = new ApexPages.StandardController(opp);
        ChangeOpptyOwnerCtrl ctrlObj = new ChangeOpptyOwnerCtrl(sc);
        
        ctrlObj.saveOwner();
        
        test.stopTest();
        
    }
    
}



can any one help me to cover catch(Exception e) lines

I am new to writing validation rules and am stuck.  I need to write a rule so that a person can not change a project status to active unless a picklist field called foundation type is filled out. This would only apply to projects that fall within certain departments.