- •Table of Contents
- •About the Author
- •About the Technical Reviewer
- •Acknowledgments
- •Software Entropy
- •Clean Code
- •C++11: The Beginning of a New Era
- •Who This Book Is For
- •Conventions Used in This Book
- •Sidebars
- •Notes, Tips, and Warnings
- •Code Samples
- •Coding Style
- •C++ Core Guidelines
- •Companion Website and Source Code Repository
- •UML Diagrams
- •The Need for Testing
- •Unit Tests
- •What About QA?
- •Rules for Good Unit Tests
- •Test Code Quality
- •Unit Test Naming
- •Unit Test Independence
- •One Assertion per Test
- •Independent Initialization of Unit Test Environments
- •Exclude Getters and Setters
- •Exclude Third-Party Code
- •Exclude External Systems
- •What Do We Do with the Database?
- •Don’t Mix Test Code with Production Code
- •Tests Must Run Fast
- •How Do You Find a Test’s Input Data?
- •Equivalence Partitioning
- •Boundary Value Analysis
- •Test Doubles (Fake Objects)
- •What Is a Principle?
- •KISS
- •YAGNI
- •It’s About Knowledge!
- •Building Abstractions Is Sometimes Hard
- •Information Hiding
- •Strong Cohesion
- •Loose Coupling
- •Be Careful with Optimizations
- •Principle of Least Astonishment (PLA)
- •The Boy Scout Rule
- •Collective Code Ownership
- •Good Names
- •Names Should Be Self-Explanatory
- •Use Names from the Domain
- •Choose Names at an Appropriate Level of Abstraction
- •Avoid Redundancy When Choosing a Name
- •Avoid Cryptic Abbreviations
- •Avoid Hungarian Notation and Prefixes
- •Avoid Using the Same Name for Different Purposes
- •Comments
- •Let the Code Tell the Story
- •Do Not Comment Obvious Things
- •Don’t Disable Code with Comments
- •Don’t Write Block Comments
- •Don’t Use Comments to Substitute Version Control
- •The Rare Cases Where Comments Are Useful
- •Documentation Generation from Source Code
- •Functions
- •One Thing, No More!
- •Let Them Be Small
- •“But the Call Time Overhead!”
- •Function Naming
- •Use Intention-Revealing Names
- •Parameters and Return Values
- •Avoid Flag Parameters
- •Avoid Output Parameters
- •Don’t Pass or Return 0 (NULL, nullptr)
- •Strategies for Avoiding Regular Pointers
- •Choose simple object construction on the stack instead of on the heap
- •In a function’s argument list, use (const) references instead of pointers
- •If it is inevitable to deal with a pointer to a resource, use a smart one
- •If an API returns a raw pointer...
- •The Power of const Correctness
- •About Old C-Style in C++ Projects
- •Choose C++ Strings and Streams over Old C-Style char*
- •Use C++ Casts Instead of Old C-Style Casts
- •Avoid Macros
- •Managing Resources
- •Resource Acquisition Is Initialization (RAII)
- •Smart Pointers
- •Unique Ownership with std::unique_ptr<T>
- •Shared Ownership with std::shared_ptr<T>
- •No Ownership, but Secure Access with std::weak_ptr<T>
- •Atomic Smart Pointers
- •Avoid Explicit New and Delete
- •Managing Proprietary Resources
- •We Like to Move It
- •What Are Move Semantics?
- •The Matter with Those lvalues and rvalues
- •rvalue References
- •Don’t Enforce Move Everywhere
- •The Rule of Zero
- •The Compiler Is Your Colleague
- •Automatic Type Deduction
- •Computations During Compile Time
- •Variable Templates
- •Don’t Allow Undefined Behavior
- •Type-Rich Programming
- •Know Your Libraries
- •Take Advantage of <algorithm>
- •Easier Parallelization of Algorithms Since C++17
- •Sorting and Output of a Container
- •More Convenience with Ranges
- •Non-Owning Ranges with Views
- •Comparing Two Sequences
- •Take Advantage of Boost
- •More Libraries That You Should Know About
- •Proper Exception and Error Handling
- •Prevention Is Better Than Aftercare
- •No Exception Safety
- •Basic Exception Safety
- •Strong Exception Safety
- •The No-Throw Guarantee
- •An Exception Is an Exception, Literally!
- •If You Can’t Recover, Get Out Quickly
- •Define User-Specific Exception Types
- •Throw by Value, Catch by const Reference
- •Pay Attention to the Correct Order of Catch Clauses
- •Interface Design
- •Attributes
- •noreturn (since C++11)
- •deprecated (since C++14)
- •nodiscard (since C++17)
- •maybe_unused (since C++17)
- •Concepts: Requirements for Template Arguments
- •The Basics of Modularization
- •Criteria for Finding Modules
- •Focus on the Domain of Your Software
- •Abstraction
- •Choose a Hierarchical Decomposition
- •Single Responsibility Principle (SRP)
- •Single Level of Abstraction (SLA)
- •The Whole Enchilada
- •Object-Orientation
- •Object-Oriented Thinking
- •Principles for Good Class Design
- •Keep Classes Small
- •Open-Closed Principle (OCP)
- •A Short Comparison of Type Erasure Techniques
- •Liskov Substitution Principle (LSP)
- •The Square-Rectangle Dilemma
- •Favor Composition over Inheritance
- •Interface Segregation Principle (ISP)
- •Acyclic Dependency Principle
- •Dependency Inversion Principle (DIP)
- •Don’t Talk to Strangers (The Law of Demeter)
- •Avoid Anemic Classes
- •Tell, Don’t Ask!
- •Avoid Static Class Members
- •Modules
- •The Drawbacks of #include
- •Three Options for Using Modules
- •Include Translation
- •Header Importation
- •Module Importation
- •Separating Interface and Implementation
- •The Impact of Modules
- •What Is Functional Programming?
- •What Is a Function?
- •Pure vs Impure Functions
- •Functional Programming in Modern C++
- •Functional Programming with C++ Templates
- •Function-Like Objects (Functors)
- •Generator
- •Unary Function
- •Predicate
- •Binary Functors
- •Binders and Function Wrappers
- •Lambda Expressions
- •Generic Lambda Expressions (C++14)
- •Lambda Templates (C++20)
- •Higher-Order Functions
- •Map, Filter, and Reduce
- •Filter
- •Reduce (Fold)
- •Fold Expressions in C++17
- •Pipelining with Range Adaptors (C++20)
- •Clean Code in Functional Programming
- •The Drawbacks of Plain Old Unit Testing (POUT)
- •Test-Driven Development as a Game Changer
- •The Workflow of TDD
- •TDD by Example: The Roman Numerals Code Kata
- •Preparations
- •The First Test
- •The Second Test
- •The Third Test and the Tidying Afterward
- •More Sophisticated Tests with a Custom Assertion
- •It’s Time to Clean Up Again
- •Approaching the Finish Line
- •Done!
- •The Advantages of TDD
- •When We Should Not Use TDD
- •TDD Is Not a Replacement for Code Reviews
- •Design Principles vs Design Patterns
- •Some Patterns and When to Use Them
- •Dependency Injection (DI)
- •The Singleton Anti-Pattern
- •Dependency Injection to the Rescue
- •Adapter
- •Strategy
- •Command
- •Command Processor
- •Composite
- •Observer
- •Factories
- •Simple Factory
- •Facade
- •The Money Class
- •Special Case Object (Null Object)
- •What Is an Idiom?
- •Some Useful C++ Idioms
- •The Power of Immutability
- •Substitution Failure Is Not an Error (SFINAE)
- •The Copy-and-Swap Idiom
- •Pointer to Implementation (PIMPL)
- •Structural Modeling
- •Component
- •Interface
- •Association
- •Generalization
- •Dependency
- •Template and Template Binding
- •Behavioral Modeling
- •Activity Diagram
- •Action
- •Control Flow Edge
- •Other Activity Nodes
- •Sequence Diagram
- •Lifeline
- •Message
- •State Diagram
- •State
- •Transitions
- •External Transitions
- •Internal Transitions
- •Trigger
- •Stereotypes
- •Bibliography
- •Index
Chapter 8 Test-Driven Development
Done!
The interesting question is this: When do we know that we are done? When the piece of software that we have to implement is finished and all requirements are satisfied? When we can discontinue running through the TDD cycle? Do we really have to test all the numbers from 1 up to 3999 each by a unit test to know that we’re done?
The simple answer: If all requirements on our piece of code have been successfully implemented, and we do not find a new unit test that would lead to new production code, we are done!
And that is exactly the case with our TDD kata. We could still add many more assertions to the test method; the test would pass each time without the necessity to change the production code. This is the way TDD “speaks” to us: “Hey, my friend, you’re done!”
The result is shown in Listing 8-25.
Listing 8-25. This Version Has Been Checked In at GitHub with the Commit Message “Done”
#include <gtest/gtest.h>
#include <string> #include <array>
int main(int argc, char** argv) { testing::InitGoogleTest(&argc, argv); return RUN_ALL_TESTS();
}
struct ArabicToRomanMapping { unsigned int arabicNumber; std::string romanNumeral;
};
const std::string arabicToRomanMappings { ArabicToRomanMapping { 1000, "M" }, ArabicToRomanMapping { 900, "CM" }, ArabicToRomanMapping { 500, "D" }, ArabicToRomanMapping { 400, "CD" }, ArabicToRomanMapping { 100, "C" },
364
Chapter 8 Test-Driven Development
ArabicToRomanMapping { |
90, |
"XC" |
}, |
ArabicToRomanMapping { |
50, |
"L" |
}, |
ArabicToRomanMapping { |
40, |
"XL" |
}, |
ArabicToRomanMapping { |
10, |
"X" |
}, |
ArabicToRomanMapping { |
9, |
"IX" |
}, |
ArabicToRomanMapping { |
5, |
"V" |
}, |
ArabicToRomanMapping { |
4, |
"IV" |
}, |
ArabicToRomanMapping { |
1, |
"I" |
} |
};
std::string convertArabicNumberToRomanNumeral(unsigned int arabicNumber) { std::string romanNumeral;
for (const auto& mapping : arabicToRomanMappings) { while (arabicNumber >= mapping.arabicNumber) {
romanNumeral += mapping.romanNumeral; arabicNumber -= mapping.arabicNumber;
}
}
return romanNumeral;
}
// Test code starts here...
class RomanNumeralAssert { public:
RomanNumeralAssert() = delete;
explicit RomanNumeralAssert(const unsigned int arabicNumber) : arabicNumberToConvert(arabicNumber) { }
void isConvertedToRomanNumeral(std::string_view expectedRomanNumeral) const {
ASSERT_EQ(expectedRomanNumeral, convertArabicNumberToRomanNumeral (arabicNumberToConvert));
}
private:
const unsigned int arabicNumberToConvert;
};
365
Chapter 8 Test-Driven Development
RomanNumeralAssert checkIf(const unsigned int arabicNumber) { return RomanNumeralAssert { arabicNumber };
}
TEST(ArabicToRomanNumeralsConverterTestCase, conversionOfArabicNumbersToRomanNumerals_Works) {
checkIf(1).isConvertedToRomanNumeral("I"); checkIf(2).isConvertedToRomanNumeral("II"); checkIf(3).isConvertedToRomanNumeral("III"); checkIf(4).isConvertedToRomanNumeral("IV"); checkIf(5).isConvertedToRomanNumeral("V"); checkIf(6).isConvertedToRomanNumeral("VI"); checkIf(9).isConvertedToRomanNumeral("IX"); checkIf(10).isConvertedToRomanNumeral("X"); checkIf(20).isConvertedToRomanNumeral("XX"); checkIf(30).isConvertedToRomanNumeral("XXX"); checkIf(33).isConvertedToRomanNumeral("XXXIII"); checkIf(37).isConvertedToRomanNumeral("XXXVII"); checkIf(50).isConvertedToRomanNumeral("L"); checkIf(99).isConvertedToRomanNumeral("XCIX"); checkIf(100).isConvertedToRomanNumeral("C"); checkIf(200).isConvertedToRomanNumeral("CC"); checkIf(300).isConvertedToRomanNumeral("CCC"); checkIf(499).isConvertedToRomanNumeral("CDXCIX"); checkIf(500).isConvertedToRomanNumeral("D"); checkIf(1000).isConvertedToRomanNumeral("M"); checkIf(2000).isConvertedToRomanNumeral("MM"); checkIf(2017).isConvertedToRomanNumeral("MMXVII"); checkIf(3000).isConvertedToRomanNumeral("MMM"); checkIf(3333).isConvertedToRomanNumeral("MMMCCCXXXIII"); checkIf(3999).isConvertedToRomanNumeral("MMMCMXCIX");
}
366