trigger AccountTrigger2 on Account ( before delete) 
{
    Account_Trigger_Handler handler = new Account_Trigger_Handler();    
    if(Trigger.IsDelete)
    {
        handler.OnDelete_Account(Trigger.old);
        
    }//End if
}//End class

public with sharing class Account_Trigger_Handler {

    public void OnDelete_Account(List<Account> acct)
    {
        //get user id for current user
        Id uid = UserInfo.getUserId();
        system.debug('User id : '+uid);
        //create a map to put in all the users who are authorized to delete
        Map<Id,Account_Delete_User__mdt> mapAcctDeleteUser = new Map<Id, Account_Delete_User__mdt>(); 
        //loop through the users who are authorized to delete and put them in the map we created just before this
        for(Account_Delete_User__mdt AcctDeleteUser : [SELECT id, UserId__c FROM Account_Delete_User__mdt])
        {
            mapAcctDeleteUser.put(AcctDeleteUser.Userid__c, AcctDeleteUser);
        }//end for
        
        //loop through the records in the trigger and see if the current user is authorized to delete.
        for(Account a: acct)
        {
            if(mapAcctDeleteUser.keyset().contains(uid)== false)
            {
            a.addError('You are not authorized to remove Accounts from Salesforce. Please email Salesforce.admin@XXXXX.net to have record removed.');
            }//end if
        }//end for           
     }//end method
  }

@isTest
public class Account_Trigger_HandlerTest {
  
    public static testMethod void OnDelete_AccountTest()
    {
        Profile p2 = [SELECT id FROM Profile WHERE Name ='Standard User'];
        
        User usr2 = new User (LastName ='Boris',
                              FirstName ='Badenov',
                              Email = 'boris.badenov@bullwinkleshow.com',
                              Username = 'boris.badenov@bullwinkleshow.com',
                              Alias = 'boris',
                              Profileid = p2.Id,
                              TimeZoneSidKey ='GMT' ,
                              LanguageLocaleKey = 'en_US',
                              EmailEncodingKey = 'UTF-8',
                              LocaleSidKey = 'en_US');
        insert usr2;
    //---------------------------------------------------------------------
    //https://ashwanisoni.wordpress.com/2017/05/02/create-or-update-custom-metadata-type-via-apex-code-salesforce-summer-17/
        // Set up custom metadata to be created in the subscriber org.
    Metadata.CustomMetadata customMetadata =  new Metadata.CustomMetadata();
    customMetadata.fullName = 'Account_Delete_User';
    customMetadata.label = 'User';

    Metadata.CustomMetadataValue customField = new Metadata.CustomMetadataValue();
    customField.field = 'UserId__c';
    customField.value = usr2.id;

    customMetadata.values.add(customField);

    Metadata.DeployContainer mdContainer = new Metadata.DeployContainer();
    mdContainer.addMetadata(customMetadata);

    // Setup deploy callback, MyDeployCallback implements
    // the Metadata.DeployCallback interface (code for
    // this class not shown in this example)
    CustomMetadataCallback callback = new CustomMetadataCallback();

    // Enqueue custom metadata deployment
    // jobId is the deployment ID
    Id jobId = Metadata.Operations.enqueueDeployment(mdContainer, callback);
    //----------------------------------------------------------------------
        Profile p = [SELECT id FROM Profile WHERE Name ='Standard User'];
        
        User usr1 = new User (LastName ='Fatale',
                              FirstName ='Natasha',
                              Email = 'natasha.fatele@bullwinkleshow.com',
                              Username = 'natasha.fatele@bullwinkleshow.com',
                              Alias = 'natas',
                              Profileid = p.Id,
                              TimeZoneSidKey ='GMT' ,
                              LanguageLocaleKey = 'en_US',
                              EmailEncodingKey = 'UTF-8',
                              LocaleSidKey = 'en_US');
        insert usr1;
        Account acct2 = New Account(Name='Snagglepuss', Type='Prospect', SSN__c = '12385678', CreatedById = usr1.id);
        insert acct2;
        Test.startTest();
            Database.DeleteResult result = Database.delete(acct2,false);
            System.assert(!result.isSuccess());
        Test.stopTest();
        
        
    }
}

public class CustomMetadataCallback implements Metadata.DeployCallback {
    public void handleResult(Metadata.DeployResult result,
                             Metadata.DeployCallbackContext context) {
        if (result.status == Metadata.DeployStatus.Succeeded) {
            System.debug('success: '+ result);
        } else {
            // Deployment was not successful
            System.debug('fail: '+ result);
        }                       
    }
//https://ashwanisoni.wordpress.com/2017/05/02/create-or-update-custom-metadata-type-via-apex-code-salesforce-summer-17/  
}