trigger LeadTrigger on Lead (before insert,before update,after insert,after update){ 
IF(Trigger.isAfter && Trigger.isupdate){
        LeadHelper.leadShareInsertUpdate(Trigger.New);

}
}

public class LeadHelper {
    public static List<LeadShare> csShareList = new List<LeadShare>();
    public static List<LeadShare> removeShareList = new List<LeadShare>();
    
    public static void leadShareInsertUpdate(List<Lead> leads){
        csShareList = new List<LeadShare>();
        removeShareList = new List<LeadShare>();
        Set<Id> ldIds = new Set<Id>();
        for( Lead cs : leads) {
            if( cs.CRM_User__c != NULL ) {
                // Create a new LeadShare object for each Lead where CRM_User__c field is not NULL.
                LeadShare csShare = new LeadShare();
                // Give Read write access to that user for this particular Lead record.
                csShare.LeadAccessLevel = 'edit';
                // Assign Lead Id of Lead record.
                csShare.LeadId = cs.id;
                // Assign user id to grant read write access to this particular Lead record.
                csShare.UserOrGroupId = cs.CRM_User__c;
                if(cs.OwnerId!= cs.CRM_User__c){
                    csShareList.add(csShare);
                }
            }
            
            ldIds.add( cs.id);
            
        }
        
        if(ldIds.size()>0){
            removeShareList = [Select id,LeadId,UserOrGroupId from LeadShare where LeadId=:ldIds AND RowCause = 'Manual'];
            if(removeShareList.size()>0){
                delete removeShareList;
            }
        }
        if(csShareList != null && csShareList.size()>0) {
            insert csShareList;
        }
    
    }
}

@istest
public class LeadTriggerTest {
        public static testMethod void MyTestMethod_To_Share_Leads() {
        Set<ID> newidsSet1 = new Set<ID>();
        Set<ID> newidsSet2 = new Set<ID>();
        List<Lead> NewLeadsList1 = new List<Lead>();
        List<Lead> NewLeadsList2 = new List<Lead>();
       Profile pf= [Select Id from profile Where Name ='Standard User']; 
        String orgId=UserInfo.getOrganizationId(); 
        String dateString=String.valueof(Datetime.now()).replace(' ','').replace(':','').replace('-',''); 
        Integer RandomId=Integer.valueOf(Math.rint(Math.random()*1000000)); 
        String uniqueName=orgId+dateString+RandomId; 
        User uu=new User(firstname = 'ABC', 
                         lastName = 'XYZ', 
                         email = uniqueName + '@test' + orgId + '.org', 
                         Username = uniqueName + '@test' + orgId + '.org', 
                         EmailEncodingKey = 'ISO-8859-1', 
                         Alias = uniqueName.substring(18, 23), 
                         TimeZoneSidKey = 'America/Los_Angeles', 
                         LocaleSidKey = 'en_US', 
                         LanguageLocaleKey = 'en_US', 
                         ProfileId = pf.Id, 
                         ManagerId= UserInfo.getUserId());
        System.runAs(uu){
            //Inserting the Leads with CRM_User__c
            for (Integer i=0;i<10;i++){
                NewLeadsList1.add(new Lead(FirstName='First',LastName='Name '+i,
                                           Email='email'+i+'@gmail.com',Company='ABSYZ',CRM_User__c=uu.Id));
            }
            insert NewLeadsList1;
            
            //get a set of all new created Lead ids
            for (Lead l : NewLeadsList1){
                newidsSet1.add(l.id);
            }
            
            //assert that 10 shares were created
            List<LeadShare> shares = [select id, Lead.FirstName from LeadShare where LeadId IN :newidsSet1 and RowCause = 'Manual' AND Lead.FirstName Like '%First%'];
            System.assertEquals(shares.size(),10);
            
            
            //Inserting the Leads with CRM_User__c is null
            for (Integer i=0;i<10;i++){
                NewLeadsList2.add(new Lead(FirstName='Name', LastName='LeadTesting'+i+orgId,
                                           Email='test'+i+'@gmail.com', Company='XYZ'));
            }
            insert NewLeadsList2;
            
            //get a set of all new created Lead ids
            for (Lead l : NewLeadsList1){
                newidsSet2.add(l.id);
            }
            //assert that 10 shares were created
            List<LeadShare> sharesList = [select id, Lead.FirstName from LeadShare where LeadId IN :newidsSet2 and RowCause = 'Manual' AND Lead.FirstName LIKE '%Name%'];
            System.assertEquals(sharesList.size(),0);
        }
    }
    

}