I added an attribute to customer entity

My goal is to have this attribute as Select (with data from another db table), but i didn't find any tuto about the source/model that i should create !!

Here is the Files : 

InstallData Vendor/Module/Setup/InstallData.php

    <?php

    namespace Vendor\Module\Setup;
    
    use Magento\Customer\Setup\CustomerSetupFactory;
    use Magento\Customer\Model\Customer;
    use Magento\Eav\Model\Entity\Attribute\Set as AttributeSet;
    use Magento\Eav\Model\Entity\Attribute\SetFactory as AttributeSetFactory;
    use Magento\Framework\Setup\InstallDataInterface;
    use Magento\Framework\Setup\ModuleContextInterface;
    use Magento\Framework\Setup\ModuleDataSetupInterface;

 

    class InstallData implements InstallDataInterface
    {
        
    /**
     * @var CustomerSetupFactory
     */
    protected $customerSetupFactory;
    
    /**
     * @var AttributeSetFactory
     */
    private $attributeSetFactory;
    
    /**
     * @param CustomerSetupFactory $customerSetupFactory
     * @param AttributeSetFactory $attributeSetFactory
     */
    public function __construct(
        CustomerSetupFactory $customerSetupFactory,
        AttributeSetFactory $attributeSetFactory
    ) {
        $this->customerSetupFactory = $customerSetupFactory;
        $this->attributeSetFactory = $attributeSetFactory;
    }
 
    
    
    public function install(ModuleDataSetupInterface $setup, ModuleContextInterface $context)
    {
        
        /** @var CustomerSetup $customerSetup */
        $customerSetup = $this->customerSetupFactory->create(['setup' => $setup]);
        
        $customerEntity = $customerSetup->getEavConfig()->getEntityType('customer');
        $attributeSetId = $customerEntity->getDefaultAttributeSetId();
        
        /** @var $attributeSet AttributeSet */
        $attributeSet = $this->attributeSetFactory->create();
        $attributeGroupId = $attributeSet->getDefaultGroupId($attributeSetId);
        
        $customerSetup->addAttribute(Customer::ENTITY, 'testfield', [
            'type' => 'varchar',
            'label' => 'Test Field',
            'input' => 'select',
            'required' => false,
            'visible' => true,
            'user_defined' => true,
            'visible_on_front' => true, 
            'global' => \Magento\Eav\Model\Entity\Attribute\ScopedAttributeInterface::SCOPE_GLOBAL,
            'source' => \Vendor\Module\Model\Customer\Attribute\Source\Test,
        ]);
        
        $attribute = $customerSetup->getEavConfig()->getAttribute(Customer::ENTITY, 'testfield')
        ->addData([
            'attribute_set_id' => $attributeSetId,
            'attribute_group_id' => $attributeGroupId,
            'used_in_forms' => ['adminhtml_customer','customer_account_create','customer_account_edit','checkout_register'],
        ]);
        
        $attribute->save();
          
      
    }
}

Source Model (Needed Code) : Vendor\Module\Model\Customer\Attribute\Source\Test

    <?php
    namespace Vendor\Module\Model\Customer\Attribute\Source;
    
    
    class Test extends \Magento\Eav\Model\Entity\Attribute\Source\Table
    {
        
        public function __construct(..........) 
    {
            ......................
        }
    
        /**
         * @return array
         */
        public function getAllOptions()
        {
            ...................
    
            return $this->_options;
        }
    
        
    }



Could any one help me how to create this source model.