Hi friends
I am using a child relationship query to update contact description fields whenever an account record is created or updated.

Apex class code & trigger code is workign fine but I am having an issue in test class. The code coverage is showing 72% .  

Apex class code;
public class Account_ContactDescription
{
    public void Update_Description(Set<Id> accountIds)
    {
                    
           list<Account> accountsWithContacts =[select Id,Name, (select Id,FirstName,LastName from Contacts) from Account 
                                                                           where Id IN : accountIds];
           
           list<Contact> contactsToUpdate=new list<Contact>();
           
           for(Account a:accountsWithContacts)   //loop through all queries 
          {
                 for(Contact convals:a.Contacts)
                {
                        convals.Description=convals.FirstName+' '+convals.LastName;
                         
                        contactsToUpdate.add(convals);
               }
           }
           
           update contactsToUpdate;
    }
}

Apex Trigger code:
trigger trg_UpdateContactDescription on Account (before Update)
{
    Account_ContactDescription c=new Account_ContactDescription();
     
    Map<Id,Account> amap = new Map<Id,Account>([select Id from Account]);
     
    Set<Id> accountIds = amap.KeySet();
     
    c.Update_Description(accountIds);
}          


Test class code:
@istest(SeeAllData=false)
private class AccountContactDescription_Test
{
    private static testmethod void validatetest()
    {
         Profile p = [SELECT Id FROM Profile WHERE Name='System Administrator']; 
         User u = new User(Alias = 'sample', Email='standarduser@testorg.com', 
         EmailEncodingKey='UTF-8', LastName='sampleLname', LanguageLocaleKey='en_US', 
         LocaleSidKey='en_US', ProfileId = p.Id, 
         TimeZoneSidKey='America/Los_Angeles', UserName='testnamesss@testorg.com');
         system.runAs(u)
         {
              Account  acn = new Account();
              acn.Name='test1';
                            
              Database.Insert(acn);
                       
                                        
              Contact con = new Contact();
              
              con.LastName='test3';
                                          
              con.FirstName='test4'; 
              
              Database.Insert(con); 
              
              acn.Name='test2';
              Database.Update(acn);     
        
         }
       }
   }

How to update the  description field but not sure how to go about it.
Can anyone pls le tme know:?

regards
sonali verma