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Working Effectively with Legacy Code

Notes by Jeremy W. Sherman, October 2013, based on:

Feathers, Michael. Working Effectively with Legacy Code. Sixth printing, July 2007.

Foreword:

• Software systems degrade into a mess.
• Requirements ALWAYS change.
• Your goal as a software developer: Create designs that tolerate change.

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Modern Legacy Systems

Presented by Robert Annett at QCon London, 14 Sep 2012.

Notes by Jeremy W. Sherman, 2013–10–13.

“Legacy”

What is legacy?

• Often an insult, but how odd, not like that in normal English (cf. inheritance).
• Also perhaps defined as “as opposed to its alternatives, it’s the software that actually works”.

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Working Effectively with Legacy Code

Michael C. Feathers

Notes by Jeremy W. Sherman, 14 Oct 2013.

Chapter 11: I need to make a change. What methods should I test?

Use effect sketches to figure out where to target your characterization tests prior to making changes. Big fan-in means a big bang for your test-writing buck.

• Prior to changing, write characterization tests to pin down existing behavior.
• Characterization test: A test that characterizes the actual behavior of a piece of code (186).

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WORKING EFFECTIVELY WITH LEGACY CODE

To me, legacy code is simply code without tests. I’ve gotten some grief for this definition. What do tests have to do with whether code is bad? To me, the answer is straightforward, and it is a point that I elaborate throughout the book: Code without tests is bad code. It doesn’t matter how well written it is; it doesn’t matter how pretty or object-oriented or well-encapsulated it is. With tests, we can change the behavior of our code quickly and verifiably. Without them, we really don’t know if our code is getting better or worse.

Chapter 1 Changing Software

Four Reasons to Change Software: For simplicity’s sake, let’s look at four primary reasons to change software.

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<?php

namespace Trovit\B2B\Redirect\Tests\integration\Controller;

class QueryStringBuilder
{
    const CONNECTOR = '&';
    const START = '/?';

    private $brand;

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<?php

namespace Trovit\B2B\Redirect\Tests\integration\Controller;

use Symfony\Bundle\FrameworkBundle\Test\WebTestCase;

class DefaultControllerTest extends WebTestCase
{
    private $client;

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(ns sunshine.disk-read
  (:require [clojure.core.async :as async :refer [>! <! go-loop chan close! <!!]]])
  (:import (java.io BufferedReader FileReader FileInputStream BufferedInputStream InputStreamReader)))

(def ten-gb-filename "ten.json")
(def one-meg (* 1024 1024))

(defn ^FileInputStream input-stream [^String fname]
  (FileInputStream. fname))

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#!/usr/bin/env bash

# Just 'brew install ffmpeg' first

set -e

INPUT=$1
OUTPUT=$2

ffmpeg -i "$INPUT" -filter_complex "[0:v]setpts=0.5*PTS[v];[0:a]atempo=2[a]" -map "[v]" -map "[a]" "$OUTPUT"

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// Use Gists to store code you would like to remember later on
console.log(window); // log the "window" object to the console