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: which_test.rb
    path of file: ./repos/vagrant/test/unit/vagrant/util
    
    the code of the file until where you have to start completion: # Copyright (c) HashiCorp, Inc.
# SPDX-License-Identifier: BUSL-1.1

require File.expand_path("../../../base", __FILE__)

require 'vagrant/util/platform'
require 'vagrant/util/which'

describe Vagrant::Util::Which do
  def tester (file_extension, test_extension, mode, &block)
    # create file in temp directory
    filename = '__vagr
    
  def tester (file_extension, test_extension, mode, &block)
    # create file in temp directory
    filename = '__vagrant_unit_test__'
    dir = Dir.tmpdir
    file = Pathname(dir) + (filename + file_extension)
    file.open("w") { |f| f.write("#") }
    file.chmod(mode)

    # set the path to the directory where the file is located
    allow(ENV).to receive(:[]).with("PATH").and_return(dir.to_s)
    block.call filename + test_extension

    file.unlink
  end