You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: DigestSHA256_test.rb
    path of file: ./repos/rbs/test/stdlib/digest
    
    the code of the file until where you have to start completion: require_relative '../test_helper'
require 'digest'
require 'digest/bubblebabble'

class DigestSHA256SingletonTest < T
    
  def test_digest
    assert_send_type '(?::String) -> ::String',
                     ::Digest::SHA256.new, :digest

    assert_send_type '(?::String) -> ::String',
                     ::Digest::SHA256.new, :digest, '_digest_'
  end