Testing email template in SFDC Anonymous Window

How to Test email template in SFDC Anonymous Window ?

Code

In normal case, we will use email Template to test our email in clicking ‘Send Test and verify merge fields’:

However, it sometimes, will have following result.

To testing email in Production env, we can use following code to test in Apex Anonymous Window.

Messaging.SingleEmailMessage mail =new Messaging.SingleEmailMessage(); 
 
//this set user Id 
mail.setTargetObjectId('005D0000008fQd4'); 
 
//This set Template Id 
mail.setTemplateId('00XD0000002J0Ma'); 
 
//this set record Id 
mail.setWhatId('a9ED00000000kNE');    
mail.setCCAddresses( new String[]{'you@email.com'}); 
mail.setBccSender(false); 
mail.setUseSignature(false); 
mail.setReplyTo('you@email.com'); 
 
mail.setSenderDisplayName('Tony Testing in Production'); 
 
mail.setSaveAsActivity(false);  
Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });

For how to use Apex Anonymous Window, you can perdorm with following path: Debug–>Open Execute Anonymous Window ( Ctrl+E).
Or view following post:

Sending email in Salesforce