def clear_env_vars(names, &block)
      save_vars = {}
      names.each do |k|
        k = k.to_s
        save_vars[k] = ENV[k]
        ENV[k] = nil
      end
      begin
        yield
      ensure
        names.each do |k|
          k = k.to_s
          ENV[k] = save_vars[k]
        end
      end
      true
    end
def clear_env_vars(names, &block)
      save_vars = {}
      names.each do |k|
        k = k.to_s
        save_vars[k] = ENV[k]
        ENV[k] = nil
      end
      begin
        yield
      ensure
        names.each do |k|
          k = k.to_s
          ENV[k] = save_vars[k]
        end
      end
      true
    end
Clears (set-to-nil) the given list of environment variables while
 executing the given block.

 @param [Array] names of variables to clear

 @yield [] called with environment cleared

 @return [TrueClass] always true