Add this Recursive Class. 

public Class checkRecursive{
    private static boolean run = true;
    public static boolean runOnce(){
        if(run){
            run=false;
            return true;
        }else{
            return run;
        }
    }
}

You Handler Class 

public class CannotDeleteAccount {
    
    public static void NoDeleteAccount(List<Account> accLst){
        system.debug('before delete trigger');
        Profile teamLeadprof = [select id,name from Profile where name = 'Team Leader' order by name limit 1];   
        Id profId = teamLeadprof.Id;
        System.debug('Profile Id of Current User : '+profId);
        Id currUser = UserInfo.getProfileId();
        for(Account acc : accLst){
            if(currUser==profId)
                acc.adderror('You Cannot delete the Account');
        }
    }    
}

You Trigger. 

Trigger accountTrigger on Account (before delete) {
    if(checkRecursive.runOnce()){
        if(Trigger.isBefore){
            System.debug('Inside the Trigger');
            CannotDeleteAccount.NoDeleteAccount(Trigger.Old);
        }
    }
}

Your Test Class :
@isTest
public class TestAccountDelete {
    static testMethod void deleteAccount() {
       
       Profile userProfile = [select name from Profile where name='Team Leader'];
       List<User> usersList = [select Name,Profile.Name from User where Profile.Name='Team Leader'];
       Account accToDelete = new Account();
       accToDelete.OwnerId = usersList[0].Id; 
       accToDelete.Rating='Hot';
       insert accToDelete;
       delete accToDelete;
    }
    public static testMethod void ValidationTest() {

      Profile p = [SELECT Id FROM Profile WHERE Name='Team Leader'];
      User u1 = new User(Alias = 'newUser', Email='newuser1@testorg.com',
         EmailEncodingKey='UTF-8', LastName='Testing', LanguageLocaleKey='en_US',
         LocaleSidKey='en_US', ProfileId = p.Id,
         TimeZoneSidKey='America/Los_Angeles', UserName='newusr@testorg.com');

      System.runAs(u1) {
         // The following code runs as user u1
         System.debug('Current User: ' + UserInfo.getUserName());
         System.debug('Current Profile: ' + UserInfo.getProfileId());
         Account ac1 = new Account(); 
         ac1.OwnerId = u1.Id; 
         ac1.Name = 'test'; 
         ac1.ratings = 'started';
         insert ac1; 
         // Verify the "You cann't delete this record" error is thrown whenever an attemp is made to delete a Account

        Boolean errorThrown = false;
        try 
        {
            delete ac1;
        } 
        catch (Exception e) 
        {
            System.debug(e);
            if (e.getMessage().contains('You can\'t delete this record')) 
            {
                errorThrown = true;
            }
        }         
      }
   }
}