Code Coverage for Catch block in test class?

Question

I'm unable to cover the code coverage for catch block.Kindly help me to cover that code lines as well.

Apex Class:

public without sharing class ZTS_EU_Contact_populateCallDates
{
        Map <id, date> mapConIdDate = new Map<id, Date>();
        Map <ID, List<Attendee__C>> mapCallAttendees = new Map<ID, List<Attendee__C>>();
        Map <id, id> mapAttcon = new Map<id, id>();
        List<Contact> listCon = new List<Contact>();
        LIst <Attendee__C> listAttendee = new List<Attendee__C>();
        List <Attendee__C> listAllAttendee = new List<Attendee__C>();
    
        public void getLastCallDate(List<Call__C> triggerNew){

            for(CAll__C oCall: [SELECT id FROM CAll__C WHERE ID IN :TriggerNew])
            {
                mapCallAttendees.put(oCall.id,null);
            }

            for(Attendee__C oAtt : [SELECT ZTS_EU_call__C, id ,ZTS_EU_Contact__C FROM Attendee__C WHERE ZTS_EU_call__c in :TriggerNew])
            {
                listAttendee.add(oAtt);
                System.debug('OATT:;;;;'+oAtt);
                List <Attendee__c> newList = mapCallAttendees.get(oAtt.ZTS_EU_call__c);
                if(newList == null) newList = new List<Attendee__C>();
                newList.add(oAtt);
                mapCallAttendees.put(oAtt.ZTS_EU_call__C, newList);
                mapAttCon.put(oAtt.id, oAtt.ZTS_EU_Contact__C );
            }
            System.debug('listAttendee:;;;;'+listAttendee);
            if(listAttendee.size() >0){

                system.debug('mapCallAttendees ::::'+ mapCallAttendees.size());
                listAttendee = [SELECT ZTS_EU_Contact__c FROM Attendee__C WHERE ZTS_EU_Call__c IN :mapCallAttendees.keyset()];
                LIst <id> listConID = new List<id>();
                for(Attendee__c oAtt: listAttendee)
                {
                    listConID.add(OAtt.ZTS_EU_Contact__c);
                }

                listAllAttendee = [SELECT id,ZTS_EU_Contact__c from Attendee__C where ZTS_EU_Contact__c IN : listConID];
                List<id> listAttID =  new List<id>();
                for(Attendee__C oAtt1: listAllAttendee)
                {
                    listAttID.add(oAtt1.id);
                    mapAttCon.put(oAtt1.id, oAtt1.ZTS_EU_Contact__C );
                }
                system.debug('mapAttCon ::::'+ mapAttCon.size());

                //Updated Query to filter only Submitted & Planned Calls - NoorbashaSheik Chanbasha - 11/18/2021 - [SC-008964]
                List <AggregateResult> results = [SELECT ZTS_EU_Contact__c con,Max(ZTS_EU_call__r.ZTS_EU_Start_Date_Time__c) date from Attendee__c WHERE ID IN: listAttID AND (ZTS_EU_call__r.ZTS_EU_Status__c= 'Submitted' OR ZTS_EU_call__r.ZTS_EU_Status__c='Completed') Group BY ZTS_EU_Contact__c];
                for(AggregateResult ar: results)
                {
                    mapConIdDate.put(String.valueOf(ar.get('con')), Date.valueOF(ar.get('date')));                    
                }
                for(Call__c oCall: triggerNew)
                {
                    for(Attendee__c oAtt : mapCallAttendees.get(oCall.id))
                    {
                        Contact oCon = new Contact();
                        oCon.id = mapAttcon.get(oAtt.id);
                        system.debug('Before assigning call :::'+ oCall.ZTS_EU_Start_Date_Time__c);
                        system.debug('Before assigning :::'+ mapConIdDate.get(oCon.id));
                        if(oCall.ZTS_EU_Start_Date_Time__c > mapConIdDate.get(oCon.id))
                        {
                            system.debug('Before assigning :::'+ mapConIdDate.get(oCon.id));
                            system.debug('call start date :::'+ oCall.ZTS_EU_Start_Date_Time__c);
                            mapConIdDate.put(oCon.ID, Date.valueOf(oCall.ZTS_EU_Start_Date_Time__c));
                            system.debug('After assigning :::'+ mapConIdDate.get(oCon.id));
                        }
                        
                    }
                }
                for(ID conId : mapConIdDate.keyset())
                {
                    system.debug('conId :::'+ conId);
                    Contact oCon = new Contact(id = conId );
                    system.debug('final date :::'+ mapConIDDate.get(conId ));
                    oCon.ZTS_EU_Last_call_Date__c = mapConIDDate.get(conId );
                    system.debug('Print Last date :::'+ oCon.ZTS_EU_Last_call_Date__c);
                    listCon.add(oCon);
                } 
                try {
                    update(listCon);
                } catch(DmlException dex) {
                    String errorMessages = '';
                    for (Integer i = 0; i < dex.getNumDml(); i++) {
                        System.debug('ZTS_EU_Contact_populateCallDates.getLastCallDate ');
                        System.debug('DML Message: ' + dex.getDmlMessage(i));
                        errorMessages += dex.getDmlMessage(i) + '\n';
                    }
                    errorMessages.removeEnd('\n');
                    ZTS_EU_Logger.notify = true;
                    ZTS_EU_Logger.error(errorMessages,null, 'ZTS_EU_Contact_populateCallDates.getLastCallDate Contact DML error');
                }

        }
    }
}

Test Class :

@isTest
public class ZTS_EU_Contact_populateCallDatesTest 
{
    static testMethod void validate_ZTS_EU_Contact_populateCallDates() {
        ZTS_DataUtilityTest.createPrimaryContactInactiveProfileCustomSetting(); 
        User usr = new User();
        usr = ZTS_EU_DataUtilityTest.createUserWithProfile('System Administrator', false);
        usr.FirstName = 'davidsUser';
        usr.zts_eu_market__c = 'United Kingdom';
        insert usr;

        System.runAs(usr)
        {
            Map <id, date> mapConIdDate = new Map<id, Date>();
            Map <ID, List<Attendee__C>> mapCallAttendees = new Map<ID, List<Attendee__C>>();
            Map <id, id> mapAttcon = new Map<id, id>();
            List<Contact> listCon = new List<Contact>();
            LIst <Attendee__C> listAttendee = new List<Attendee__C>();
            List <Attendee__C> listAllAttendee = new List<Attendee__C>();

            ZTS_EU_Contact_populateCallDates popdates= new ZTS_EU_Contact_populateCallDates();
            List<Contact> contactList=ZTS_EU_DataUtilityTest1.createContactRecord(1);
            contactList[0].ZTS_EU_Market__c = 'United Kingdom';
            insert contactList;
            test.startTest();
            List<Call__c> callList = ZTS_EU_DataUtilityTest1.createCallRecord(1);
            insert callList;

            List<Attendee__c> attenList=new List<Attendee__c>();
            //List<Attendee__c> attenList=ZTS_EU_DataUtilityTest1.createAttendee(1);
            //insert attenList;
            Attendee__c attendee = new Attendee__c();
            attendee.ZTS_EU_Contact__c = contactList[0].Id;
            attendee.ZTS_EU_call__c = callList[0].Id;
            attenList.add(attendee);
            insert attenList;
            //mapCallAttendees.put(callList[0].id,attenList);
            popdates.getLastCAllDate(callList);
            test.stopTest();
        }
    }
}

Answer 1

The general solution for coercing an exception is via dependency injection of a mock object that replaces a runtime object where the mock object:

• sets a field value such that the DML will fail
• throws an exception when the mock object is invoked

This requires restructuring your code into Separation of Concerns patterns. A sophisticated one is the fflib pattern along with apexmocks but others exist as well.

A way to wrap your head around this is to use the HttpCalloutMock as an example. In a testmethod, SFDC will invoke your mock callout responder.

What you'll need is to restructure your code to use a ContactUpdater object that you can mock at testmethod time, injecting it into the code-under-test. Such mock ContactUpdater object could null out the Contact.LastName thus coercing a DML exception (as LastName is a schema-required field)

Answer 2

We can use validation rules here. Check Contact validation rules which can fire at contact update. Create contact with those values which will be used to fire validation rule. So you can get DML exception here.

if you don't have any validation rules to fire at Contact update. try to move these exception block code to separate method in the class and use it test class. I know it is not a good practice but this is the way to get good test class coverage.

try{
// use any DML and it should fail here
}catch(DMLException ex) {
 // call the new method which will have exception code.
}