Working Effectively with Legacy Code - M. Feathers
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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 moth 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
PART II: Changing Software ................................. .55
Chapter 6:1 Don't Have Much Time and I Have to Change It. .... 57
Sprout Method .........................................59
Sprout Class 63
Wrap Method ......................................... 67
Wrap Class .71
Summary. ............. ............................... 76
Chapter 7: It Takes Forever to Make a Change 77
Understanding .77
Lag Time .78
Breaking Dependencies . .79
Summary 85
Chapter 8: How Do I Add a Feature? 87
Test-Driven Development (TDD) 88
Programming by Difference 94
Summary 104
Chapter 9:1 Can’t Get This Class into a Test Harness ................ 105
The Case of the Irritating Parameter ....................... 106
The Case of the Hidden Dependency ...................... .113
The Case of the Construction Blob 116
The Case of the Irritating Global Dependency .118
The Case of the Horrible Include Dependencies .127
The Case of the Onion Parameter ......................... 130
The Case of the Aliased Parameter 133
Chapter 10:1 Can’t Run This Method in a Test Harness .............. 137
The Case ot the Hidden Method . 138
The Case of the “Helpful” Language Feature ................ . 141
The Case of the Undetectable Side Effect . .144
Chapter 11:1 Need to Make a Change. What Methods Should I Test? ... 151
Reasoning About Effects ............................... . 151
Reasoning Forward .................................... 157
Effect Propagation 163
Tools for Effect Reasoning ............................... 165
Learning from Effect Analysis ........................... .167
Simplifying Effect Sketches . 168
Chapter 12:1 Need to Make Many Changes in One Area.............. 173
Interception Points .................................... 174
Judging Design with Pinch Points ......................... 182
Pinch Point Traps ..184
Chapter 13:1 Need to Make a Change,
but I Don’t Know What Tests to Write 185
Characterization Tests 186
Characterizing Classes 189
Targeted Testing 190
A Heuristic for Writing Characterization Tests 195
Chapter 14: Dependencies on Libraries Are Killing Me 197
Chapter 15: My Application Is All API Calls 199
Chapter 16:1 Don’t Understand the Code Well Enough to Change It .... 209
Notes/Sketching 210
Listing Markup 211
Scratch Refactoring 212
Delete Unused Code ................................... 213
Chapter 17: My Application Has No Structure ..................... 215
Telling the Story of the System ........................... 216
Naked CRC ......................................... 220
Conversation Scrutiny ................................. 224
Chapter 18: My Test Code Is in the Way .......................... 227
Class Naming Conventions .............................. 227
Test Location ........................................ 228
Chapter 19: My Project Is Not Object Oriented.
How Do I Make Safe Changes?. ....................... 231
An Easy Case ........................................ 232
A Hard Case 232
Adding New Behavior 236
Taking Advantage of Object Orientation ................... 239
It’s All Object Oriented 242
Chapter 20: This Class Is Too Big and I Don’t Want It to Get Any Bigger . 245
Seeing Responsibilities . 249
Other Techniques ......................................265
Moving Forward .265
After Extract Class .268
Chapter 21: I’m Changing the Same Code All Over the Place .......... 269
First Steps .......................................... .272
Chapter 22:1 Need to Change a Monster Method
and I Can’t Write Tests for It ......... 289
Varieties of Monsters ................................... 290
Tackling Monsters with Automated Refactoring Support ...... .294
The Manual Refactoring Challenge .297
Strategy 304
Chapter 23: How Do I Know That I’m Not Breaking Anything? 309
Hyperaware Editing .310
Single-Goal Editing 311
Preserve Signatures 312
Lean on the Compiler 315
Chapter 24: We Feel Overwhelmed. It Isn’t Going to Get Any Better. .... .319
PART III: Dependency-Breaking Techniques ................... .323
Chapter 25: Dependency-Breaking Techniques ..................... 325
Adapt Parameter ..................................... .326
Break Out Method Object .330
Definition Completion .337
Encapsulate Global References .339
Expose Static Method .345
Extract and Override Call .348
Extract and Override Factory Method ..................... .350
Extract and Override Getter .352
Extract Implementer .................................. .356
Extract Interface 362
Introduce Instance Delegator ............................ .369
Introduce Static Setter ................................. .372-
Link Substitution ..................................... .377
Parameterize Constructor .379
Parameterize Method .................................. .383
Primitivize Parameter .................................. 385
Pull Up Feature 388
Push Down Dependency ................................ 392
Replace Function with Function Pointer .................... 396
Replace Global Reference with Getter ..................... 399
Subclass and Override Method . 401
Supersede Instance Variable 404
Template Redefinition .408
Text Redefinition .412
Appendix: Refactoring 415
Extract Method 415
Glossary 421
Index 423
