Effective Unit Testing

Transcription

1 Effective Unit Testing A guide forjava developers LASSE KOSKELA 11 MANNING Shelter Island

2 contents xv preface acknowledgments xvii about this book xix about the cover illustration xxiv Part 1 Foundations 1 The promise ofgood tests State of the union: writing better tests The value of having tests 5 Factors ofproductivity 8 The curve of design potential Tests as a design tool 10 Test-driven development 11 Behavior-driven development Summary 14 In search ofgood Readable code is maintainable code Structure helps make sense of things It's not good if it's testing the wrong things Independent tests run easily in solitude 21 ix

3 X CONTENTS 2.5 Reliable tests are reliable Every trade has its tools and tests are no exception Summary 26 Test doubles The power of a test double 28 Isolating the code under test 28 Speeding up Making execution deterministic 31 Simulating special conditions 32 Exposing hidden information 32 test execution Types of test doubles 33 Test stubs are unusually short things 34 Fake objects do it without side effects 35 Test spies steal your secrets 36 Mock objects object to surprises Guidelines for using test doubles 39 Pick the right double for the test 40 Arrange, act, assert 40 Check for behavior, not implementation 42 Choose your tools 42 Inject your dependencies Summary 44 Part 2 Catalog 45 Readability Primitive assertions 48 Example 48 What to do about it? 49 Summary Hyperassertions 51 Example 51 What to do about it 1 54 Summary Bitwise assertions 56 Example 56 What to do about it? 56 Summary Incidental details 57 Example 57 What to do about it? 58 Summary Split personality 60 Example 61 What to do about it? Split logic 64 Summary Magic Example 65 What to do about it? 66 Summary 69 numbers 70 Example 70 What to do about it? 71 Summary 71

4 CONTENTS 4.8 Setup sermon 72 Example 72 What to do about it? 73 Summary Overprotective tests 75 Example 75 What to do about it? 76 Summary Summary 76 Maintainability Duplication 79 Example 79 What to do about it? 80 Summary Conditional logic 82 Example 83 What to do about it? 83 Summary Flaky test 85 Example 85 What to do about it? 86 Summary Crippling file path 88 Example 88 What to do about it? 89 Summary Persistent temp files 91 Example 91 What to do about it? 92 Summary Sleeping snail 94 Example 94 What to do about it? 95 Summary Pixel perfection 97 Example 97 What to do about it? 98 Summary Parameterized mess 102 Example 103 What to do about it? 106 Summary Lack of cohesion in methods 108 Example 109 What to do about it? 110 Summary Summary 113 Trustworthiness Commented-out tests 116 Example 116 What to do about it? 117 Summary Misleading comments 118 Example 118 Wfiat to do about it? 119 Summary Never-failing tests 121 Example 121 What to do about it? 122 Summary 123

5 xii CONTENTS 6.4 Shallow promises 123 Example(s) 123 What to do about it"? 125 Summary Lowered expectations 127 Example 127 What to do about it? 128 Summary Platform prejudice 129 Example 129 What to do about it? 130 Summary Conditional tests 133 Example 133 Wliat to do about it? 134 Summary Summary 135 Part 3 Diversions 137 Testable design What's testable design? Testability Modular design 140 SOLID design principles 141 Modular design in context 143 Test-driving toward modular design 143 issues 143 Can't instantiate a class 144 Can't invoke a method 144 Can't observe the outcome 145 Can't substitute a collaborator 145 Can't override a method Guidelines for testable design 146 Avoid complex private methods 146 Avoid final methods 147 Avoid static methods 148 Use new with care 148 Avoid logic in constructors 149 Avoid the Singleton 150 Favor composition over inheritance. 151 Wrap external libraries 152 Avoid service lookups Summary 154 %) Writing tests in other JVM languages 156 f ^ 8.1 The premise of mixing JVM languages 157 General benefits 157 Writing tests Writing unit tests with Groovy 160 Simplified setup for tests 161 Groovier JUnit 4 tests 163

6 CONTENTS xiii 8.3 Expressive power with BDD tools 163 Groovy specs with easyb 164 Spock Framework: steroids for writing more expressive tests 165 Spock Framework's test doubles are on steroids, too Summary 168 Speeding up test execution Looking for a speed-up 171 The need for speed 171 Approaching the situation 172 Profiling a build 172 Profiling 9.2 Speeding up test code 178 tests 175 Don't sleep unless you 're tired 178 Beware the bloated base class 179 Watch out for redundant setup and teardown 181 Be picky about who you invite to your test 182 Stay local, stay fast 183 Resist the temptation to hit the database 184 There's no slower I/O than file I/O Speeding up the build 187 Faster I/O with a RAM disk 188 Parallelizing the build 189 Offload to a higher-powered CPU 194 Distribute the build Summary 200 appendix A appendix B JUnit primer 202 ExtendingJUnit 209 index 217