new_contents: import pytest
  
  from mollie.api.error import IdentifierError
  from mollie.api.resources.base import ResourceBase
  
  
  class MyTestResource(ResourceBase):
      """Minimal resource for testing."""
  
      RESOURCE_ID_PREFIX = "test_"
  
  
  def test_validate_resource_id(client):
      resource = MyTestResource(client)
      with pytest.raises(IdentifierError) as excinfo:
          resource.validate_resource_id("invalid")
  
      assert str(excinfo.value) == "Invalid Identifier 'invalid', it should start with 'test_'."
  
  
  def test_validate_resource_id_custom_identifier_name(client):
      resource = MyTestResource(client)
      with pytest.raises(IdentifierError) as excinfo:
          resource.validate_resource_id("invalid", name="MockerMockMock")
  
      assert str(excinfo.value) == "Invalid MockerMockMock 'invalid', it should start with 'test_'."
  
  
  def test_validate_resource_id_custom_message(client):
      resource = MyTestResource(client)
      with pytest.raises(IdentifierError) as excinfo:
          resource.validate_resource_id("invalid", message="No no no, only tests allowed here!")
  
      assert str(excinfo.value) == "No no no, only tests allowed here!"
  
subject: Add tests for validate_resource_id()