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If you're looking for a practical resource on Test-Driven Development this is the book for you. You've found a practical end-to-end guide that will help you implement Test-Driven Techniques for your software development projects.
The goal of this book is to teach you iOS development using Swift in a manageable way without overwhelming you. We focus only on the essentials and cover the material in a hands-on practice manner for you to code along.
It provides a unique view inside the software running on iOS, the operating system that powers the Apple iPhone and iPad. You will explore the hidden second life your phone leads, wherein it is a full-fledged computer and software development platform.
This book will help you understand the process of Test-driven development (TDD) and how it impacts your applications written in Swift. Through practical, real-world examples, you'll start seeing how to implement TDD in context.
This book is a Fake Book for iOS developers about Test-Driven Development. You cannot learn Test-Driven Development from this book. Use it to look up how to implement many test cases encountered in iOS development.
Xcode sets up a completely ready project for development in addition to a test target for your unit tests. Open the FirstDemoTests folder in Project Navigator. Within the folder, there are two files: FirstDemoTests.swift and Info.plist. Select FirstDemoTests.swift to open it in the editor.
You can download the example code files for all Packt books you have purchased from your account at If you purchased this book elsewhere, you can visit and register to have the files e-mailed directly to you.
The green diamond with a checkmark on the left-hand side of the editor indicates that the test passed. So, this is it. This is your first unit test. Step back for a moment and celebrate. This could be the beginning of a new development paradigm for you.
In 1996, Kent Beck introduced a new software development methodology called Extreme Programming. The word "extreme" indicates that the concepts behind Extreme Programming are totally different from the concepts used in software development back then. It was based on 12 rules or practices.
This so called Test-First Programming leads to Test-Driven Development. As the name suggests, in TDD, tests drive development. This means that the developer writes code only because there is a test that fails. The tests dictate whether code has to be written, and they also provide a measure when a feature is implemented: it is implemented when all tests for this feature pass.
Often the simplest implementation will not be enough for the feature you try to implement but still enough to make all the tests pass. This just means that you need another failing test to further drive the development of the feature.
"Core Data 1.0 is not perfect, but it is a rock solid product that I'm damned proud of. The quality and performance achieved could not have been done without the use of unit testing. Furthermore, we were able to perform highly disruptive operations to the codebase very late in the development cycle. The end result was a vast increase in performance, a much cleaner code base, and rock solid release."
In practice, it's not that easy. For example, should the position and color of a button be tested? Should the view hierarchy be tested? Probably not. The color and exact position of the button are not important for the functioning of an app. In the early stages of development, these kind of things tend to change. With Auto Layout and different localizations of the app, the exact position of buttons and labels depend on many parameters.
In addition to this, you should not test the whole application in total using unit tests. Unit tests are meant to test small units of computation. They need to be fast and reliable. Things, such as database access and networking, should be tested using integration tests, where the tests drive the real finished application. Integration tests are allowed to be slow because they are run a lot less often than unit tests. Usually, they are run at the end of the development before the application is released, or they are run with the help of a continues integration system each night on a server where it doesn't matter that the complete test suite takes several minutes to execute.
Dr. Dominik Hauser completed his PhD in physics from the University of Heidelberg. While working as a university professor, he started iOS development in his spare time. His first app on physics has been an astounding success worldwide. Since then, he has turned himself into a full-time iOS developer, with a number of successful apps to his name. He has been a Swift developer since day one and runs a blog on iOS development.
Test-driven development (TDD) is a software development process relying on software requirements being converted to test cases before software is fully developed, and tracking all software development by repeatedly testing the software against all test cases. This is as opposed to software being developed first and test cases created later.
There are various aspects to using test-driven development, for example the principles of "keep it simple, stupid" (KISS) and "You aren't gonna need it" (YAGNI). By focusing on writing only the code necessary to pass tests, designs can often be cleaner and clearer than is achieved by other methods. In Test-Driven Development by Example, Kent Beck also suggests the principle "Fake it till you make it".
Each test case fails initially: This ensures that the test really works and can catch an error. Once this is shown, the underlying functionality can be implemented. This has led to the "test-driven development mantra", which is "red/green/refactor", where red means fail and green means pass. Test-driven development constantly repeats the steps of adding test cases that fail, passing them, and refactoring. Receiving the expected test results at each stage reinforces the developer's mental model of the code, boosts confidence and increases productivity.
Test-driven development offers more than just simple validation of correctness, but can also drive the design of a program. By focusing on the test cases first, one must imagine how the functionality is used by clients (in the first case, the test cases). So, the programmer is concerned with the interface before the implementation. This benefit is complementary to design by contract as it approaches code through test cases rather than through mathematical assertions or preconceptions.
Test-driven development offers the ability to take small steps when required. It allows a programmer to focus on the task at hand as the first goal is to make the test pass. Exceptional cases and error handling are not considered initially, and tests to create these extraneous circumstances are implemented separately. Test-driven development ensures in this way that all written code is covered by at least one test. This gives the programming team, and subsequent users, a greater level of confidence in the code.
While it is true that more code is required with TDD than without TDD because of the unit test code, the total code implementation time could be shorter based on a model by Müller and Padberg. Large numbers of tests help to limit the number of defects in the code. The early and frequent nature of the testing helps to catch defects early in the development cycle, preventing them from becoming endemic and expensive problems. Eliminating defects early in the process usually avoids lengthy and tedious debugging later in the project.
Because no more code is written than necessary to pass a failing test case, automated tests tend to cover every code path. For example, for a TDD developer to add an else branch to an existing if statement, the developer would first have to write a failing test case that motivates the branch. As a result, the automated tests resulting from TDD tend to be very thorough: they detect any unexpected changes in the code's behaviour. This detects problems that can arise where a change later in the development cycle unexpectedly alters other functionality.
Test-driven development does not perform sufficient testing in situations where full functional tests are required to determine success or failure, due to extensive use of unit tests. Examples of these are user interfaces, programs that work with databases, and some that depend on specific network configurations. TDD encourages developers to put the minimum amount of code into such modules and to maximize the logic that is in testable library code, using fakes and mocks to represent the outside world.
Management support is essential. Without the entire organization believing that test-driven development is going to improve the product, management may feel that time spent writing tests is wasted.
Unit tests created in a test-driven development environment are typically created by the developer who is writing the code being tested. Therefore, the tests may share blind spots with the code: if, for example, a developer does not realize that certain input parameters must be checked, most likely neither the test nor the code will verify those parameters. Another example: if the developer misinterprets the requirements for the module they are developing, the code and the unit tests they write will both be wrong in the same way. Therefore, the tests will pass, giving a false sense of correctness.
Test-driven development has been adopted outside of software development, in both product and service teams, as test-driven work. For testing to be successful, it needs to be practiced at the micro and macro levels. Every method in a class, every input data value, log message, and error code, amongst other data points, need to be tested. Similar to TDD, non-software teams develop quality control (QC) checks (usually manual tests rather than automated tests) for each aspect of the work prior to commencing. These QC checks are then used to inform the design and validate the associated outcomes. The six steps of the TDD sequence are applied with minor semantic changes: 2b1af7f3a8