Working Effectively with Legacy Code

Cover......Page 1
Contents......Page 8
Foreword......Page 14
Preface......Page 16
Introduction......Page 22
PART I: The Mechanics of Change......Page 24
  Four Reasons to Change Software......Page 26
  Risky Change......Page 30
 Chapter 2: Working with Feedback......Page 32
  What Is Unit Testing?......Page 35
  Test Coverings......Page 37
  The Legacy Code Change Algorithm......Page 41
 Chapter 3: Sensing and Separation......Page 44
  Faking Collaborators......Page 46
  A Huge Sheet of Text......Page 52
  Seams......Page 53
  Seam Types......Page 56
  Automated Refactoring Tools......Page 68
  Mock Objects......Page 70
  Unit-Testing Harnesses......Page 71
  General Test Harnesses......Page 76
PART II: Changing Software......Page 78
 Chapter 6: I Don’t Have Much Time and I Have to Change It.......Page 80
  Sprout Method......Page 82
  Sprout Class......Page 86
  Wrap Method......Page 90
  Wrap Class......Page 94
  Summary......Page 99
  Understanding......Page 100
  Lag Time......Page 101
  Breaking Dependencies......Page 102
  Summary......Page 108
 Chapter 8: How Do I Add a Feature?......Page 110
  Test-Driven Development (TDD)......Page 111
  Programming by Difference......Page 117
  Summary......Page 127
 Chapter 9: I Can’t Get This Class into a Test Harness......Page 128
  The Case of the Irritating Parameter......Page 129
  The Case of the Hidden Dependency......Page 136
  The Case of the Construction Blob......Page 139
  The Case of the Irritating Global Dependency......Page 141
  The Case of the Horrible Include Dependencies......Page 150
  The Case of the Onion Parameter......Page 153
  The Case of the Aliased Parameter......Page 156
 Chapter 10: I Can’t Run This Method in a Test Harness......Page 160
  The Case of the Hidden Method......Page 161
  The Case of the “Helpful” Language Feature......Page 164
  The Case of the Undetectable Side Effect......Page 167
  Reasoning About Effects......Page 174
  Reasoning Forward......Page 180
  Effect Propagation......Page 186
  Tools for Effect Reasoning......Page 188
  Learning from Effect Analysis......Page 190
  Simplifying Effect Sketches......Page 191
 Chapter 12: I Need to Make Many Changes in One Area......Page 196
  Interception Points......Page 197
  Judging Design with Pinch Points......Page 205
  Pinch Point Traps......Page 207
 Chapter 13: I Need to Make a Change, but I Don’t Know What Tests to Write......Page 208
  Characterization Tests......Page 209
  Characterizing Classes......Page 212
  Targeted Testing......Page 213
  A Heuristic for Writing Characterization Tests......Page 218
 Chapter 14: Dependencies on Libraries Are Killing Me......Page 220
 Chapter 15: My Application Is All API Calls......Page 222
 Chapter 16: I Don’t Understand the Code Well Enough to Change It......Page 232
  Notes/Sketching......Page 233
  Listing Markup......Page 234
  Scratch Refactoring......Page 235
  Delete Unused Code......Page 236
 Chapter 17: My Application Has No Structure......Page 238
  Telling the Story of the System......Page 239
  Naked CRC......Page 243
  Conversation Scrutiny......Page 247
  Class Naming Conventions......Page 250
  Test Location......Page 251
 Chapter 19: My Project Is Not Object Oriented. How Do I Make Safe Changes?......Page 254
  A Hard Case......Page 255
  Adding New Behavior......Page 259
  Taking Advantage of Object Orientation......Page 262
  It’s All Object Oriented......Page 265
 Chapter 20: This Class Is Too Big and I Don’t Want It to Get Any Bigger......Page 268
  Seeing Responsibilities......Page 272
  Moving Forward......Page 288
  After Extract Class......Page 291
 Chapter 21: I’m Changing the Same Code All Over the Place......Page 292
  First Steps......Page 295
 Chapter 22: I Need to Change a Monster Method and I Can’t Write Tests for It......Page 312
  Varieties of Monsters......Page 313
  Tackling Monsters with Automated Refactoring Support......Page 317
  The Manual Refactoring Challenge......Page 320
  Strategy......Page 327
 Chapter 23: How Do I Know That I’m Not Breaking Anything?......Page 332
  Hyperaware Editing......Page 333
  Single-Goal Editing......Page 334
  Preserve Signatures......Page 335
  Lean on the Compiler......Page 338
 Chapter 24: We Feel Overwhelmed. It Isn’t Going to Get Any Better......Page 342
PART III: Dependency-Breaking Techniques......Page 346
 Chapter 25: Dependency-Breaking Techniques......Page 348
  Adapt Parameter......Page 349
  Break Out Method Object......Page 353
  Definition Completion......Page 360
  Encapsulate Global References......Page 362
  Expose Static Method......Page 368
  Extract and Override Call......Page 371
  Extract and Override Factory Method......Page 373
  Extract and Override Getter......Page 375
  Extract Implementer......Page 379
  Extract Interface......Page 385
  Introduce Instance Delegator......Page 392
  Introduce Static Setter......Page 395
  Link Substitution......Page 400
  Parameterize Constructor......Page 402
  Parameterize Method......Page 406
  Primitivize Parameter......Page 408
  Pull Up Feature......Page 411
  Push Down Dependency......Page 415
  Replace Function with Function Pointer......Page 419
  Replace Global Reference with Getter......Page 422
  Subclass and Override Method......Page 424
  Supersede Instance Variable......Page 427
  Template Redefinition......Page 431
  Text Redefinition......Page 435
 Extract Method......Page 438
Glossary......Page 444
 B......Page 446
 C......Page 447
 D......Page 448
 F......Page 449
 I......Page 450
 M......Page 451
 P......Page 453
 R......Page 454
 S......Page 455
 T......Page 456
 X......Page 457