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Файл:Tomek Kaczanowski - Practical Unit Testing with JUnit and Mockito - 2013.pdf
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- •Practical Unit Testing with JUnit and Mockito
- •Table of Contents
- •About the Author
- •Acknowledgments
- •Preface
- •Preface - JUnit
- •Part I. Developers' Tests
- •Chapter 1. On Tests and Tools
- •1.1. An Object-Oriented System
- •1.2. Types of Developers' Tests
- •1.2.1. Unit Tests
- •1.2.2. Integration Tests
- •1.2.3. End-to-End Tests
- •1.2.4. Examples
- •1.2.5. Conclusions
- •1.3. Verification and Design
- •1.5. Tools Introduction
- •Chapter 2. Unit Tests
- •2.1. What is a Unit Test?
- •2.2. Interactions in Unit Tests
- •2.2.1. State vs. Interaction Testing
- •2.2.2. Why Worry about Indirect Interactions?
- •Part II. Writing Unit Tests
- •3.2. Class To Test
- •3.3. Your First JUnit Test
- •3.3.1. Test Results
- •3.4. JUnit Assertions
- •3.5. Failing Test
- •3.6. Parameterized Tests
- •3.6.1. The Problem
- •3.6.2. The Solution
- •3.6.3. Conclusions
- •3.7. Checking Expected Exceptions
- •3.8. Test Fixture Setting
- •3.8.1. Test Fixture Examples
- •3.8.2. Test Fixture in Every Test Method
- •3.8.3. JUnit Execution Model
- •3.8.4. Annotations for Test Fixture Creation
- •3.9. Phases of a Unit Test
- •3.10. Conclusions
- •3.11. Exercises
- •3.11.1. JUnit Run
- •3.11.2. String Reverse
- •3.11.3. HashMap
- •3.11.4. Fahrenheits to Celcius with Parameterized Tests
- •3.11.5. Master Your IDE
- •Templates
- •Quick Navigation
- •Chapter 4. Test Driven Development
- •4.1. When to Write Tests?
- •4.1.1. Test Last (AKA Code First) Development
- •4.1.2. Test First Development
- •4.1.3. Always after a Bug is Found
- •4.2. TDD Rhythm
- •4.2.1. RED - Write a Test that Fails
- •How To Choose the Next Test To Write
- •Readable Assertion Message
- •4.2.2. GREEN - Write the Simplest Thing that Works
- •4.2.3. REFACTOR - Improve the Code
- •Refactoring the Tests
- •Adding Javadocs
- •4.2.4. Here We Go Again
- •4.3. Benefits
- •4.4. TDD is Not Only about Unit Tests
- •4.5. Test First Example
- •4.5.1. The Problem
- •4.5.2. RED - Write a Failing Test
- •4.5.3. GREEN - Fix the Code
- •4.5.4. REFACTOR - Even If Only a Little Bit
- •4.5.5. First Cycle Finished
- •‘The Simplest Thing that Works’ Revisited
- •4.5.6. More Test Cases
- •But is It Comparable?
- •Comparison Tests
- •4.6. Conclusions and Comments
- •4.7. How to Start Coding TDD
- •4.8. When not To Use Test-First?
- •4.9. Should I Follow It Blindly?
- •4.9.1. Write Good Assertion Messages from the Beginning
- •4.9.2. If the Test Passes "By Default"
- •4.10. Exercises
- •4.10.1. Password Validator
- •4.10.2. Regex
- •4.10.3. Booking System
- •Chapter 5. Mocks, Stubs, Test Spies
- •5.1. Introducing Mockito
- •5.1.1. Creating Test Doubles
- •5.1.2. Expectations
- •5.1.3. Verification
- •5.1.4. Conclusions
- •5.2. Types of Test Double
- •5.2.1. Code To Be Tested with Test Doubles
- •5.2.2. The Dummy Object
- •5.2.3. Test Stub
- •5.2.4. Test Spy
- •5.2.5. Mock
- •5.3. Putting it All Together
- •5.4. Example: TDD with Test Doubles
- •5.4.2. The Second Test: Send a Message to Multiple Subscribers
- •Refactoring
- •5.4.3. The Third Test: Send Messages to Subscribers Only
- •5.4.4. The Fourth Test: Subscribe More Than Once
- •Mockito: How Many Times?
- •5.4.5. The Fifth Test: Remove a Subscriber
- •5.4.6. TDD and Test Doubles - Conclusions
- •More Test Code than Production Code
- •The Interface is What Really Matters
- •Interactions Can Be Tested
- •Some Test Doubles are More Useful than Others
- •5.5. Always Use Test Doubles… or Maybe Not?
- •5.5.1. No Test Doubles
- •5.5.2. Using Test Doubles
- •No Winner So Far
- •5.5.3. A More Complicated Example
- •5.5.4. Use Test Doubles or Not? - Conclusion
- •5.6. Conclusions (with a Warning)
- •5.7. Exercises
- •5.7.1. User Service Tested
- •5.7.2. Race Results Enhanced
- •5.7.3. Booking System Revisited
- •5.7.4. Read, Read, Read!
- •Part III. Hints and Discussions
- •Chapter 6. Things You Should Know
- •6.1. What Values To Check?
- •6.1.1. Expected Values
- •6.1.2. Boundary Values
- •6.1.3. Strange Values
- •6.1.4. Should You Always Care?
- •6.1.5. Not Only Input Parameters
- •6.2. How to Fail a Test?
- •6.3. How to Ignore a Test?
- •6.4. More about Expected Exceptions
- •6.4.1. The Expected Exception Message
- •6.4.2. Catch-Exception Library
- •6.4.3. Testing Exceptions And Interactions
- •6.4.4. Conclusions
- •6.5. Stubbing Void Methods
- •6.6. Matchers
- •6.6.1. JUnit Support for Matcher Libraries
- •6.6.2. Comparing Matcher with "Standard" Assertions
- •6.6.3. Custom Matchers
- •6.6.4. Advantages of Matchers
- •6.7. Mockito Matchers
- •6.7.1. Hamcrest Matchers Integration
- •6.7.2. Matchers Warning
- •6.8. Rules
- •6.8.1. Using Rules
- •6.8.2. Writing Custom Rules
- •6.9. Unit Testing Asynchronous Code
- •6.9.1. Waiting for the Asynchronous Task to Finish
- •6.9.2. Making Asynchronous Synchronous
- •6.9.3. Conclusions
- •6.10. Testing Thread Safe
- •6.10.1. ID Generator: Requirements
- •6.10.2. ID Generator: First Implementation
- •6.10.3. ID Generator: Second Implementation
- •6.10.4. Conclusions
- •6.11. Time is not on Your Side
- •6.11.1. Test Every Date (Within Reason)
- •6.11.2. Conclusions
- •6.12. Testing Collections
- •6.12.1. The TDD Approach - Step by Step
- •6.12.2. Using External Assertions
- •Unitils
- •Testing Collections Using Matchers
- •6.12.3. Custom Solution
- •6.12.4. Conclusions
- •6.13. Reading Test Data From Files
- •6.13.1. CSV Files
- •6.13.2. Excel Files
- •6.14. Conclusions
- •6.15. Exercises
- •6.15.1. Design Test Cases: State Testing
- •6.15.2. Design Test Cases: Interactions Testing
- •6.15.3. Test Collections
- •6.15.4. Time Testing
- •6.15.5. Redesign of the TimeProvider class
- •6.15.6. Write a Custom Matcher
- •6.15.7. Preserve System Properties During Tests
- •6.15.8. Enhance the RetryTestRule
- •6.15.9. Make an ID Generator Bulletproof
- •Chapter 7. Points of Controversy
- •7.1. Access Modifiers
- •7.2. Random Values in Tests
- •7.2.1. Random Object Properties
- •7.2.2. Generating Multiple Test Cases
- •7.2.3. Conclusions
- •7.3. Is Set-up the Right Thing for You?
- •7.4. How Many Assertions per Test Method?
- •7.4.1. Code Example
- •7.4.2. Pros and Cons
- •7.4.3. Conclusions
- •7.5. Private Methods Testing
- •7.5.1. Verification vs. Design - Revisited
- •7.5.2. Options We Have
- •7.5.3. Private Methods Testing - Techniques
- •Reflection
- •Access Modifiers
- •7.5.4. Conclusions
- •7.6. New Operator
- •7.6.1. PowerMock to the Rescue
- •7.6.2. Redesign and Inject
- •7.6.3. Refactor and Subclass
- •7.6.4. Partial Mocking
- •7.6.5. Conclusions
- •7.7. Capturing Arguments to Collaborators
- •7.8. Conclusions
- •7.9. Exercises
- •7.9.1. Testing Legacy Code
- •Part IV. Listen and Organize
- •Chapter 8. Getting Feedback
- •8.1. IDE Feedback
- •8.1.1. Eclipse Test Reports
- •8.1.2. IntelliJ IDEA Test Reports
- •8.1.3. Conclusion
- •8.2. JUnit Default Reports
- •8.3. Writing Custom Listeners
- •8.4. Readable Assertion Messages
- •8.4.1. Add a Custom Assertion Message
- •8.4.2. Implement the toString() Method
- •8.4.3. Use the Right Assertion Method
- •8.5. Logging in Tests
- •8.6. Debugging Tests
- •8.7. Notifying The Team
- •8.8. Conclusions
- •8.9. Exercises
- •8.9.1. Study Test Output
- •8.9.2. Enhance the Custom Rule
- •8.9.3. Custom Test Listener
- •8.9.4. Debugging Session
- •Chapter 9. Organization Of Tests
- •9.1. Package for Test Classes
- •9.2. Name Your Tests Consistently
- •9.2.1. Test Class Names
- •Splitting Up Long Test Classes
- •Test Class Per Feature
- •9.2.2. Test Method Names
- •9.2.3. Naming of Test-Double Variables
- •9.3. Comments in Tests
- •9.4. BDD: ‘Given’, ‘When’, ‘Then’
- •9.4.1. Testing BDD-Style
- •9.4.2. Mockito BDD-Style
- •9.5. Reducing Boilerplate Code
- •9.5.1. One-Liner Stubs
- •9.5.2. Mockito Annotations
- •9.6. Creating Complex Objects
- •9.6.1. Mummy Knows Best
- •9.6.2. Test Data Builder
- •9.6.3. Conclusions
- •9.7. Conclusions
- •9.8. Exercises
- •9.8.1. Test Fixture Setting
- •9.8.2. Test Data Builder
- •Part V. Make Them Better
- •Chapter 10. Maintainable Tests
- •10.1. Test Behaviour, not Methods
- •10.2. Complexity Leads to Bugs
- •10.3. Follow the Rules or Suffer
- •10.3.1. Real Life is Object-Oriented
- •10.3.2. The Non-Object-Oriented Approach
- •Do We Need Mocks?
- •10.3.3. The Object-Oriented Approach
- •10.3.4. How To Deal with Procedural Code?
- •10.3.5. Conclusions
- •10.4. Rewriting Tests when the Code Changes
- •10.4.1. Avoid Overspecified Tests
- •10.4.2. Are You Really Coding Test-First?
- •10.4.3. Conclusions
- •10.5. Things Too Simple To Break
- •10.6. Conclusions
- •10.7. Exercises
- •10.7.1. A Car is a Sports Car if …
- •10.7.2. Stack Test
- •Chapter 11. Test Quality
- •11.1. An Overview
- •11.2. Static Analysis Tools
- •11.3. Code Coverage
- •11.3.1. Line and Branch Coverage
- •11.3.2. Code Coverage Reports
- •11.3.3. The Devil is in the Details
- •11.3.4. How Much Code Coverage is Good Enough?
- •11.3.5. Conclusion
- •11.4. Mutation Testing
- •11.4.1. How does it Work?
- •11.4.2. Working with PIT
- •11.4.3. Conclusions
- •11.5. Code Reviews
- •11.5.1. A Three-Minute Test Code Review
- •Size Heuristics
- •But do They Run?
- •Check Code Coverage
- •Conclusions
- •11.5.2. Things to Look For
- •Easy to Understand
- •Documented
- •Are All the Important Scenarios Verified?
- •Run Them
- •Date Testing
- •11.5.3. Conclusions
- •11.6. Refactor Your Tests
- •11.6.1. Use Meaningful Names - Everywhere
- •11.6.2. Make It Understandable at a Glance
- •11.6.3. Make Irrelevant Data Clearly Visible
- •11.6.4. Do not Test Many Things at Once
- •11.6.5. Change Order of Methods
- •11.7. Conclusions
- •11.8. Exercises
- •11.8.1. Clean this Mess
- •Appendix A. Automated Tests
- •A.1. Wasting Your Time by not Writing Tests
- •A.1.1. And what about Human Testers?
- •A.1.2. One More Benefit: A Documentation that is Always Up-To-Date
- •A.2. When and Where Should Tests Run?
- •Appendix B. Running Unit Tests
- •B.1. Running Tests with Eclipse
- •B.1.1. Debugging Tests with Eclipse
- •B.2. Running Tests with IntelliJ IDEA
- •B.2.1. Debugging Tests with IntelliJ IDEA
- •B.3. Running Tests with Gradle
- •B.3.1. Using JUnit Listeners with Gradle
- •B.3.2. Adding JARs to Gradle’s Tests Classpath
- •B.4. Running Tests with Maven
- •B.4.1. Using JUnit Listeners and Reporters with Maven
- •B.4.2. Adding JARs to Maven’s Tests Classpath
- •Appendix C. Test Spy vs. Mock
- •C.1. Different Flow - and Who Asserts?
- •C.2. Stop with the First Error
- •C.3. Stubbing
- •C.4. Forgiveness
- •C.5. Different Threads or Containers
- •C.6. Conclusions
- •Appendix D. Where Should I Go Now?
- •Bibliography
- •Glossary
- •Index
- •Thank You!
Chapter 1. On Tests and Tools
This introductory chapter presents the main categories of test. It will enable us to understand the role of each of them, and also to see the place and purpose of unit tests.
Naming Chaos
If you start digging into the topic of tests, you will be amazed at how many names show up. Unit tests, integration tests, smoke tests, stress tests, end-to-end tests, exploratory tests, system tests, performance tests, user tests, automated tests, acceptance tests, etc. You may well feel perplexed by the sheer number of them, and by the variety of existing classifications. You will get even more perplexed if you start looking for a definition for each of them. Soon you will come across a good few definitions of the same term that differ substantially1. This terminological chaos makes testing subjects much harder to follow than they should be.
In this book I follow what I regard as being the most widely used set of test-related terms. I think, that the chosen names describe their purpose well. I can only hope that they do so for you too.
1.1. An Object-Oriented System
We will right away discuss three kinds of tests that are essential for developers: unit tests (which are the main topic of this book), integration tests and end-to-end tests. Because the object-oriented (OO) programming paradigm2 is dominant in the Java world, we will learn what role each of these tests plays in the testing of an OO system. Figure 1.1 presents a very simple abstraction of such a system. (We will get on to the meaning of "workers" and "managers" very soon.)
Figure 1.1. An OO system abstraction
Yes, that is it! A bunch of circles and arrows. Circles are objects, arrows are messages being passed between them. As you can see, we also have a client in this picture, and his action (his request) has initiated a great deal of activity in our OO system. Why so many objects, and so many messages, out
1Alas, even though some terms seem to have a well-established meaning, they still often get to be misused. 2See http://en.wikipedia.org/wiki/Object-oriented_programming for more information.
2
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