def diff_files(expected, relative_path, &block)
        produced = temp_transformed_path + relative_path
        Diff.new(expected, produced, relative_path, &block)
      end
def diff_files(expected, relative_path, &block)
        produced = temp_transformed_path + relative_path
        Diff.new(expected, produced, relative_path, &block)
      end
Compares two files to check if they are identical and produces a clear diff
 to highlight the differences.

 @param  [Pathname] expected
         The file in the after directory

 @param  [Pathname] relative_path
         The file in the temp directory

 @param  [Block<(Pathname)->(to_s)>] block
         the block, which transforms the files in a better comparable form

 @return [Diff]
         An object holding a diff