Add helper to get sample schemas for use in tests
user
```ruby
require "schema/field_definitions"
require "schema/document_types"

def schema_dir
  File.expand_path('../config/schema', File.dirname(__FILE__))
end

def sample_field_definitions(fields=nil)
  @sample_field_definitions ||= FieldDefinitionParser.new(schema_dir).parse
  if fields.nil?
    @sample_field_definitions
  else
    @sample_field_definitions.select { |field, _|
      fields.include?(field)
    }
  end
end

def sample_document_types
  @sample_document_types ||= DocumentTypesParser.new(schema_dir, sample_field_definitions).parse
end
```
assistant