class Test::Unit::Assertions::AssertionMessage

def max_diff_target_string_size
  return @@max_diff_target_string_size if @@max_diff_target_string_size
  size = ENV["TEST_UNIT_MAX_DIFF_TARGET_STRING_SIZE"]
  if size
    begin
      size = Integer(size)
    rescue ArgumentError
      size = nil
    end
  end
  size || MAX_DIFF_TARGET_STRING_SIZE
end