Hello, I wrote a trigger to check if the url = 'https://sig-cb--Full.cs88.my.salesforce.com' and the profile of the current user is a specific profile (SIG-FSM-Super User) and if so the trigger shows an error message and also an image which I included in the addError function, it looks like this:

trigger ContactCreationForServiceMaxUsers on Contact (Before insert) {
   
       String baseURL = String.valueof(URL.getSalesforceBaseUrl());
      
       system.debug('<<baseURL>>' + baseURL);
       Boolean isBaseURL = baseURL.contains('https://sig-cb--Full.cs88.my.salesforce.com');
       System.debug(' >> String.valueof(URL.getSalesforceBaseUrl()) >>'+baseURL ); 
       User currentUser = [SELECT Id, Profile.Name FROM USER WHERE Id =:UserInfo.getUserId()]; 
      
       Contact c = new Contact(); 
      
       System.debug(' >> isBaseURL >>'+isBaseURL ); 
       System.debug(' >> currentUser.Profile.Name>>'+currentUser.Profile.Name ); 
   
     for(Contact c : Trigger.New){ 
          if(isBaseURL == TRUE  && currentUser.Profile.Name == 'SIG-FSM-Super User'){
           c.addError(' <p style="color:red; font-size: 20px;">Service contact creation is only allowed from “Account” tab using the blue button “Create Contact” after selecting a account”</p><img id="theImage" src="https://sig-cb--full--c.cs88.content.force.com/servlet/servlet.FileDownload?file=0159E0000002tNp" width="850px" height="100px" alt="Description of image here"/> ', false); 
          } 
     } 
}

Can anyone help me with how to build the test class for the trigger? At least theoretical.

1. First I need to create a contact
2. I need to create a user with a profile = 'super-user'
3. somehow i need to check the addError function..

Something like this...