Growing Object-Oriented Software, Guided by Tests Book

Foreword xv

Preface xvii

Acknowledgments xxi

About the Authors xxiii

PART I: INTRODUCTION 1

Chapter 1: What Is the Point of Test-Driven Development? 3

Software Development as a Learning Process 3

Feedback Is the Fundamental Tool 4

Practices That Support Change 5

Test-Driven Development in a Nutshell 6

The Bigger Picture 7

Testing End-to-End 8

Levels of Testing 9

External and Internal Quality 10

Chapter 2: Test-Driven Development with Objects 13

A Web of Objects 13

Values and Objects 13

Follow the Messages 14

Tell, Don’t Ask 17

But Sometimes Ask 17

Unit-Testing the Collaborating Objects 18

Support for TDD with Mock 19

Chapter 3: An Introduction to the Tools 21

Stop Me If You’ve Heard This One Before 21

A Minimal Introduction to JUnit 4 21

Hamcrest Matchers and assertThat() 24

jMock2: Mock Objects 25

PART II: THE PROCESS OF TEST-DRIVEN DEVELOPMENT 29

Chapter 4: Kick-Starting the Test-Driven Cycle 31

Introduction 31

First, Test a Walking Skeleton 32

Deciding the Shape of the Walking Skeleton 33

Build Sources of Feedback 35

Expose Uncertainty Early 36

Chapter 5: Maintaining the Test-Driven Cycle 39

Introduction 39

Start Each Feature with an Acceptance Test 39

Separate Tests That Measure Progress from Those That Catch Regressions 40

Start Testing with the Simplest Success Case 41

Write the Test That You’d Want to Read 42

Watch the Test Fail 42

Develop from the Inputs to the Outputs 43

Unit-Test Behavior, Not Methods 43

Listen to the Tests 44

Tuning the Cycle 45

Chapter 6: Object-Oriented Style 47

Introduction 47

Designing for Maintainability 47

Internals vs. Peers 50

No And’s, Or’s, or But’s 51

Object Peer Stereotypes 52

Composite Simpler Than the Sum of Its Parts 53

Context Independence 54

Hiding the Right Information 55

An Opinionated View 56

Chapter 7: Achieving Object-Oriented Design 57

How Writing a Test First Helps the Design 57

Communication over Classification 58

Value Types 59

Where Do Objects Come From? 60

Identify Relationships with Interfaces 63

Refactor Interfaces Too 63

Compose Objects to Describe System Behavior 64

Building Up to Higher-Level Programming 65

And What about Classes? 67

Chapter 8: Building on Third-Party Code 69

Introduction 69

Only Mock Types That You Own 69

Mock Application Objects in Integration Tests 71

PART III: A WORKED EXAMPLE 73

Chapter 9: Commissioning an Auction Sniper 75

To Begin at the Beginning 75

Communicating with an Auction 78

Getting There Safely 79

This Isn’t Real 81

Chapter 10: The Walking Skeleton 83

Get the Skeleton out of the Closet 83

Our Very First Test 84

Some Initial Choices 86

Chapter 11: Passing the First Test 89

Building the Test Rig 89

Failing and Passing the Test 95

The Necessary Minimum 102

Chapter 12: Getting Ready to Bid 105

An Introduction to the Market 105

A Test for Bidding 106

The AuctionMessageTranslator 112

Unpacking a Price Message 118

Finish the Job 121

Chapter 13: The Sniper Makes a Bid 123

Introducing AuctionSniper 123

Sending a Bid 126

Tidying Up the Implementation 131

Defer Decisions 136

Emergent Design 137

Chapter 14: The Sniper Wins the Auction 139

First, a Failing Test 139

Who Knows about Bidders? 140

The Sniper Has More to Say 143

The Sniper Acquires Some State 144

The Sniper Wins 146

Making Steady Progress 148

Chapter 15: Towards a Real User Interface 149

A More Realistic Implementation 149

Displaying Price Details 152

Simplifying Sniper Events 159

Follow Through 164

Final Polish 168

Observations 171

Chapter 16: Sniping for Multiple Items 175

Testing for Multiple Items 175

Adding Items through the User Interface 183

Observations 189

Chapter 17: Teasing Apart Main 191

Finding a Role 191

Extracting the Chat 192

Extracting the Connection 195

Extracting the SnipersTableModel 197

Observations 201

Chapter 18: Filling In the Details 205

A More Useful Application 205

Stop When We’ve Had Enough 205

Observations 212

Chapter 19: Handling Failure 215

What If It Doesn’t Work? 215

Detecting the Failure 217

Displaying the Failure 218

Disconnecting the Sniper 219

Recording the Failure 221

Observations 225

PART IV: SUSTAINABLE TEST-DRIVEN DEVELOPMENT 227

Chapter 20: Listening to the Tests 229

Introduction 229

I Need to Mock an Object I Can’t Replace (without Magic) 230

Logging Is a Feature 233

Mocking Concrete Classes 235

Don’t Mock Values 237

Bloated Constructor 238

Confused Object 240

Too Many Dependencies 241

Too Many Expectations 242

What the Tests Will Tell Us (If We’re Listening) 244

Chapter 21: Test Readability 247

Introduction 247

Test Names Describe Features 248

Canonical Test Structure 251

Streamline the Test Code 252

Assertions and Expectations 254

Literals and Variables 255

Chapter 22: Constructing Complex Test Data 257

Introduction 257

Test Data Builders 258

Creating Similar Objects 259

Combining Builders 261

Emphasizing the Domain Model with Factory Methods 261

Removing Duplication at the Point of Use 262

Communication First 264

Chapter 23: Test Diagnostics 267

Design to Fail 267

Small, Focused, Well-Named Tests 268

Explanatory Assertion Messages 268

Highlight Detail with Matchers 268

Self-Describing Value 269

Obviously Canned Value 270

Tracer Object 270

Explicitly Assert That Expectations Were Satisfied 271

Diagnostics Are a First-Class Feature 271

Chapter 24: Test Flexibility 273

Introduction 273

Test for Information, Not Representation 274

Precise Assertions 275

Precise Expectations 277

“Guinea Pig” Objects 284

PART V: ADVANCED TOPICS 287

Chapter 25: Testing Persistence 289

Introduction 289

Isolate Tests That Affect Persistent State 290

Make Tests Transaction Boundaries Explicit 292

Testing an Object That Performs Persistence Operations 294

Testing That Objects Can Be Persisted 297

But Database Tests Are S-l-o-w! 300

Chapter 26: Unit Testing and Threads 301

Introduction 301

Separating Functionality and Concurrency Policy 302

Unit-Testing Synchronization 306

Stress-Testing Passive Objects 311

Synchronizing the Test Thread with Background Threads 312

The Limitations of Unit Stress Tests 313

Chapter 27: Testing Asynchronous Code 315

Introduction 315

Sampling or Listening 316

Two Implementations 318

Runaway Tests 322

Lost Updates 323

Testing That an Action Has No Effect 325

Distinguish Synchronizations and Assertions 326

Externalize Event Sources 326

Afterword: A Brief History of Mock Objects 329

Appendix A: jMock2 Cheat Sheet 335

Appendix B: Writing a Hamcrest Matcher 343

Bibliography 347

Index 349