Working Effectively with Legacy Code.pdf

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Contents

Foreword

Preface

Introduction

PART I: The Mechanics of Change

Chapter 1: Changing Software

Four Reasons to Change Software

Risky Change

Chapter 2: Working with Feedback

What Is Unit Testing?

Higher-Level Testing

Test Coverings

The Legacy Code Change Algorithm

Chapter 3: Sensing and Separation

Faking Collaborators

Chapter 4: The Seam Model

A Huge Sheet of Text

Seams

Seam Types

Chapter 5: Tools

Automated Refactoring Tools

Mock Objects

Unit-Testing Harnesses

General Test Harnesses

PART II: Changing Software

Chapter 6: I Don’t Have Much Time and I Have to Change It

Sprout Method

Sprout Class

Wrap Method

Wrap Class

Summary

Chapter 7: It Takes Forever to Make a Change

Understanding

Lag Time

Breaking Dependencies

Summary

Chapter 8: How Do I Add a Feature?

Test-Driven Development (TDD)

Programming by Difference

Summary

Chapter 9: I Can’t Get This Class into a Test Harness

The Case of the Irritating Parameter

The Case of the Hidden Dependency

The Case of the Construction Blob

The Case of the Irritating Global Dependency

The Case of the Horrible Include Dependencies

The Case of the Onion Parameter

The Case of the Aliased Parameter

Chapter 10: I Can’t Run This Method in a Test Harness

The Case of the Hidden Method

The Case of the “Helpful” Language Feature

The Case of the Undetectable Side Effect

Chapter 11: I Need to Make a Change. What Methods Should I Test?

Reasoning About Effects

Reasoning Forward

Effect Propagation

Tools for Effect Reasoning

Learning from Effect Analysis

Simplifying Effect Sketches

Chapter 12: I Need to Make Many Changes in One Area

Interception Points

Judging Design with Pinch Points

Pinch Point Traps

Chapter 13: I Need to Make a Change, but I Don’t Know What Tests to Write

Characterization Tests

Characterizing Classes

Targeted Testing

A Heuristic for Writing Characterization Tests

Chapter 14: Dependencies on Libraries Are Killing Me

Chapter 15: My Application Is All API Calls

Chapter 16: I Don’t Understand the Code Well Enough to Change It

Notes/Sketching

Listing Markup

Scratch Refactoring

Delete Unused Code

Chapter 17: My Application Has No Structure

Telling the Story of the System

Naked CRC

Conversation Scrutiny

Chapter 18: My Test Code Is in the Way

Class Naming Conventions

Test Location

Chapter 19: My Project Is Not Object Oriented How Do I Make Safe Changes?

An Easy Case

A Hard Case

Adding New Behavior

Taking Advantage of Object Orientation

It’s All Object Oriented

Chapter 20: This Class Is Too Big and I Don’t Want It to Get Any Bigger

Seeing Responsibilities

Other Techniques

Moving Forward

After Extract Class

Chapter 21: I’m Changing the Same Code All Over the Place

First Steps

Chapter 22: I Need to Change a Monster Method and I Can’t Write Tests for It

Varieties of Monsters

Tackling Monsters with Automated Refactoring Support

The Manual Refactoring Challenge

Strategy

Chapter 23: How Do I Know That I’m Not Breaking Anything?

Hyperaware Editing

Single-Goal Editing

Preserve Signatures

Lean on the Compiler

Chapter 24: We Feel Overwhelmed. It Isn’t Going to Get Any Better

PART III: Dependency-Breaking Techniques

Chapter 25: Dependency-Breaking Techniques

Adapt Parameter

Break Out Method Object

Definition Completion

Encapsulate Global References

Expose Static Method

Extract and Override Call

Extract and Override Factory Method

Extract and Override Getter

Extract Implementer

Extract Interface

Introduce Instance Delegator

Introduce Static Setter

Link Substitution

Parameterize Constructor

Parameterize Method

Primitivize Parameter

Pull Up Feature

Push Down Dependency

Replace Function with Function Pointer

Replace Global Reference with Getter

Subclass and Override Method

Supersede Instance Variable

Template Redefinition

Text Redefinition

Appendix: Refactoring

Extract Method

Glossary

Index

ptg9926858From the Library of Brian Watterson

Working Effectively with Legacy Code

Robert C. Martin Series This series is directed at software developers, team-leaders, business analysts, and managers who want to increase their skills and proﬁciency to the level of a Master Craftsman. The series contains books that guide software professionals in the principles, patterns, and practices of programming, software project management, requirements gathering, design, analysis, testing, and others. ptg9926858From the Library of Brian Watterson

Working Effectively with Legacy Code Michael C. Feathers Prentice Hall Professional Technical Reference Upper Saddle River, NJ 07458 www,phptr.com ptg9926858From the Library of Brian Watterson

The authors and publisher have taken care in the preparation of this book, but make no expressed or implied warranty of any kind and assume no responsibil- ity for errors or omissions. No liability is assumed for incidental or consequen- tial damages in connection with or arising out of the use of the information or programs contained herein. Publisher: John Wait Editor in Chief: Don O’Hagan Acquisitions Editor: Paul Petralia Editorial Assistant: Michelle Vincenti Marketing Manager: Chris Guzikowski Publicist: Kerry Guiliano Cover Designer: Sandra Schroeder Managing Editor: Gina Kanouse Senior Project Editor: Lori Lyons Copy Editor: Krista Hansing Indexer: Lisa Stumpf Compositor: Karen Kennedy Proofreader: Debbie Williams Manufacturing Buyer: Dan Uhrig Prentice Hall offers excellent discounts on this book when ordered in quantity for bulk purchases or special sales, which may include electronic versions and/or custom covers and content particular to your business, training goals, marketing focus, and branding in- terests. For more information, please contact: U. S. Corporate and Government Sales 1-800-382-3419 corpsales@pearsontechgroup.com For sales outside the U. S., please contact: International Sales 1-317-428-3341 international@pearsontechgroup.com Visit us on the web: www.phptr.com Library of Congress Cataloging-in-Publication Data: 2004108115 Copyright © 2005 Pearson Education, Inc. Publishing as Prentice Hall PTR All rights reserved. Printed in the United States of America. This publication is protected by copyright, and permission must be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permissions, write to: Pearson Education, Inc. Rights and Contracts Department One Lake Street Upper Saddle River, NJ 07458 Other product or company names mentioned herein are the trademarks or registered trademarks of their respective owners. ISBN 0-13-117705-2 Text printed in the United States on recycled paper at Phoenix Book Tech. First printing, September 2004 ptg9926858From the Library of Brian Watterson

For Ann, Deborah, and Ryan, the bright centers of my life. — Michael ptg9926858From the Library of Brian Watterson

This page intentionally left blank ptg9926858From the Library of Brian Watterson

CONTENTS vii Contents Foreword by Robert C. Martin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi PART I: The Mechanics of Change. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Chapter 1: Changing Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Four Reasons to Change Software . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Risky Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Chapter 2: Working with Feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 What Is Unit Testing? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Higher-Level Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Test Coverings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 The Legacy Code Change Algorithm . . . . . . . . . . . . . . . . . . . . . . . 18 Chapter 3: Sensing and Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Faking Collaborators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Chapter 4: The Seam Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 A Huge Sheet of Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Seams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Seam Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Chapter 5: Tools. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Automated Refactoring Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Mock Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Unit-Testing Harnesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 General Test Harnesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 ptg9926858From the Library of Brian Watterson

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