Hi,
I developed a trigger that automatize the process of assigment of users in public groups, and I created the test class too, but occurs an error of DML and Query.

Hete is the trigger code.
trigger User_Public_Group on User (before insert, before update) {
    
    if(trigger.isBefore){
        GroupMember publicGroup = new GroupMember();
        if(trigger.isInsert){
           for(User u : trigger.new){
               if(u.ProfileId == '00e16000001GkRp' || u.ProfileId == '00e16000001GkRk' || u.ProfileId == '00e16000001GkS4'){
                    publicGroup.GroupId = '00GA0000000U7Cs';
                    publicGroup.UserOrGroupId = u.Id;
                    Database.insert(publicGroup);
               }else if(u.ProfileId == '00e16000001GkRf' || u.ProfileId == '00e16000001GkKU' || u.ProfileId == '00e16000001GkRz'){
                   publicGroup.GroupId = '00G16000005ReMc';
                   publicGroup.UserOrGroupId = u.Id;
                   Database.insert(publicGroup);
               }
           }
        }
        if(trigger.isUpdate){
           for(User u : trigger.new){
             if(u.ProfileId == '00e16000001GkRp' || u.ProfileId == '00e16000001GkRk' || u.ProfileId == '00e16000001GkS4'){
                     publicGroup.GroupId = '00GA0000000U7Cs';
                    publicGroup.UserOrGroupId = u.Id;
                    Database.insert(publicGroup);
               }else if(u.ProfileId == '00e16000001GkRf' || u.ProfileId == '00e16000001GkKU' || u.ProfileId == '00e16000001GkRz'){
                   publicGroup.GroupId = '00G16000005ReMc';
                   publicGroup.UserOrGroupId = u.Id;
                   Database.insert(publicGroup);
               }
           }
        }
    }
}


Hete is teh test code

@isTest
public class Teste_User_Public_Group {
    
    @isTest
    public static void criarUsuarioArquiteto(){
       User thisUser = [SELECT Id FROM User WHERE Id = :UserInfo.getUserId()];
        User user;
        Account a;
        
        Group gp = new Group(Name = 'Teste');
        insert gp;
        
        a = [SELECT Id, Name FROM Account WHERE Name = 'Comunidade Service IT - Comercial'];
        
        Contact con = new Contact (FirstName='Teste1', LastName='Teste2', AccountId = a.Id);
        insert con;
        
        System.runAs (thisUser){
        user = new User(ContactID = con.Id,  FirstName = 'Test', LastName='User2', ProfileId = '00e16000001GkKU', Username = 'Teste@teste.com', Email= 'Teste@teste.com', Alias ='teste', EmailEncodingKey='UTF-8', LocaleSidKey='en_US', LanguageLocaleKey='en_US', TimeZoneSidKey='America/Los_Angeles', UserRoleId='00E1600000156aP');
        insert user;
        
        GroupMember gpm = new GroupMember();
        gpm.GroupId = gp.Id;
        gpm.UserOrGroupId = user.Id;
        Database.insert(gpm);
        } 
    }
    @isTest
    public static void criarUsuarioVendedor(){      
        
        Group gp = new Group(Name = 'Teste');
        insert gp;
        
        Account a = new Account(Name = 'Test Account', Regional__c = 'SP');
        insert a;
        
        Contact con = new Contact (FirstName='Teste1', LastName='Teste2', AccountId = a.Id);
        insert con;

        User user = new User(ContactID = con.Id, FirstName = 'Test', LastName='User2', ProfileId = '00e16000001GkKU', Username = 'Teste@teste.com', Email= 'Teste@teste.com', Alias ='teste', EmailEncodingKey='UTF-8', LocaleSidKey='en_US', LanguageLocaleKey='en_US', TimeZoneSidKey='America/Los_Angeles', UserRoleId='00E1600000156aP');
        insert user;
        
        GroupMember gpm = new GroupMember();
        gpm.GroupId = gp.Id;
        gpm.UserOrGroupId = user.Id;
        Database.insert(gpm);
        
    }
    
    @isTest
    public static void atualizarUsuario(){
        Group gp = new Group(Name = 'Teste');
        insert gp;
        
        Account a = new Account(Name = 'Test Account', Regional__c = 'SP');
        insert a;
        
        Contact con = new Contact (FirstName='Teste1', LastName='Teste2', AccountId = a.Id);
        insert con;

        User user = new User(ContactID = con.Id, FirstName = 'Test', LastName='User2', ProfileId = '00e16000001GkKU', Username = 'Teste@teste.com', Email= 'Teste@teste.com', Alias ='teste', EmailEncodingKey='UTF-8', LocaleSidKey='en_US', LanguageLocaleKey='en_US', TimeZoneSidKey='America/Los_Angeles', UserRoleId='00E1600000156aP');
        insert user;
        
        User u = [SELECT Id, ProfileId FROM User Where Id = : user.Id];
        u.ProfileId='00e16000001GkKU';
        update u;
    }
}

here is the message error that show.
System.DmlException: Insert failed. First exception on row 0; first error: MIXED_DML_OPERATION,
System.QueryException: List has no rows for assignment to SObject
System.DmlException: Insert failed. First exception on row 0; first error: MIXED_DML_OPERATION,

Can someone help me?

Thanks

Rafael