Trigger Class >>>>>>>>

rigger TriggerOnUser on User (before update) {

    HandlerClass_User.userisDeactivated(trigger.new, trigger.oldMap);
}

Handler Class >>>>>>>>>

public class HandlerClass_User {

    public static void userisDeactivated(list<User> newUser, Map<Id,User>OldMap){
        set<Id> setOfDeactivedIds = new Set<Id>();
        Map<Id,list<PermissionSetAssignment>> userPSAMap = new Map<Id,list<PermissionSetAssignment>>();        
        list<PermissionSetAssignment> PSAuserDelete = new list<PermissionSetAssignment>();        
        for(User u : newUser){
            if(u.IsActive == false && u.IsActive != OldMap.get(u.Id).IsActive){
                setOfDeactivedIds.add(u.id);
                system.debug('Deactived User Id is'+u.id);
            }
        }
        
        list<PermissionSetAssignment> listOfPremissionSetAssign = [SELECT Id, AssigneeId,PermissionSetId,PermissionSet.Name  from PermissionSetAssignment
                                                Where AssigneeId IN : setOfDeactivedIds AND Permissionset.IsOwnedByProfile =false];
        List<PermissionSetLicenseAssign> permSetsLiceUsers = [SELECT Id, AssigneeId from PermissionSetLicenseAssign where AssigneeId IN: setOfDeactivedIds];
        List<GroupMember> grpMemUsers = [SELECT Id, GroupId, UserOrGroupId FROM GroupMember WHERE UserorGroupId IN : setOfDeactivedIds]; 
        for(User u:newUser){
            if(u.IsActive == false && u.IsActive != OldMap.get(u.Id).IsActive){
                for(PermissionSetAssignment psa : listOfPremissionSetAssign){
                    if(psa.AssigneeId == u.id){
                        if(userPSAMap.containsKey(u.id)){
                            userPSAMap.get(u.id).add(psa);
                        }
                        else{
                            userPSAMap.put(u.id, new list<PermissionSetAssignment> {psa});
                        }
                    }
                }
                
               }
        }
        
        system.debug('Get user Id and PSA'+userPSAMap);
        
        for(User u: newUser){
            if(u.IsActive == false && u.IsActive != OldMap.get(u.Id).IsActive){
                if(userPSAMap.containsKey(u.id)){
                    PSAuserDelete.addAll(userPSAMap.get(u.id));
                }
                              
            }
        }
        system.debug('List Of PSA to Delete for Users'+PSAuserDelete);
        
    
    if(!PSAuserDelete.isEmpty()){
        delete PSAuserDelete;
    }
    
        
}
}

Test Class >>>>>>>>>>>>

@isTest
public class TestHandlerClass_User {

    @isTest
    public static void TestDeactiveUser(){
        Profile p = [SELECT Id,Name FROM Profile where Name='sys Admin'];
        UserRole u1 =[SELECT Id,Name FROM UserRole where Name='Manager'];
        
        User u = new User(UserName='kallam.salesforce132@gmail.com', Alias = 'rkall', Email='kallam.salesforce12@gmail.com', 
                          EmailEncodingKey='UTF-8', LastName='Kallam', LanguageLocaleKey='en_US', 
                          LocaleSidKey='en_US',ProfileId = p.Id,UserRoleId =u1.id,TimeZoneSidKey='America/Los_Angeles',isActive =true);
       // insert u;
        list<User> lu = new List<User>();
        lu.add(u);   
        insert lu;
        system.debug('list users'+lu);
        system.debug('list users'+lu[0].id);
         Id AssiId = lu[0].id;
        Map<Id,User> Mu = new Map<Id,User>();
        Mu.put(lu[0].id, lu[0]);
        system.debug('Map Key'+ Mu.keySet());        
        
        list<PermissionSetAssignment> lpsa = [SELECT Id, AssigneeId, PermissionSetId,PermissionSet.Name FROM PermissionSetAssignment where PermissionSet.Name like '%Assign%'];
          List<PermissionSetAssignment> psl = new List<PermissionSetAssignment>();
            PermissionSetAssignment psa =new PermissionSetAssignment(PermissionSetId = lpsa[0].PermissionSetId, AssigneeId = lu[0].Id);
            psl.add(psa);
            insert psl;  
        
        lu[0].IsActive= false;
        update lu;
        
      //  HandlerClass_User hc = new HandlerClass_User();
        HandlerClass_User.userisDeactivated(lu,Mu);
       List<PermissionSetAssignment> lpsa1 = [SELECT Id, AssigneeId,PermissionSetId,PermissionSet.Name  from PermissionSetAssignment where AssigneeId =: Mu.keySet() ];
         system.debug('****'+lpsa1.size());
         System.assertEquals(lpsa1.isEmpty(), true);
            
        
         
    }
    
}