Test-driven development (TDD) instructs developers to add new lines of code only if an automated test did not pass. This helps to avoid duplicating code and make it clean and bug-free. It’s one of the main parts of tests and integrations in the development cycle

Characteristics of test-driven development (TDD)

Mindset is key to the test development process. TDD involves changing one’s mindset with a focus on proving the functionality, validation, as well as processing of the object by specific algorithms. It is why the question of testing should be asked at the development stage, which eliminates the need for “after tests.”

Changing the mindset offers the effectiveness of test development. First, one should assess the business logic for which the developer is responsible. Second, one needs to validate interfaces and abstract classes to avoid rewriting the code completely for new client requests. Third, it is crucial to test third-party code wrappers like the “adapter” and “trade” patterns. Fourth, it is necessary to examine the design patterns.

REST API and data providers also require testing, especially for data rate, validation, and code status. The same applies to error and “throws” handlers to ensure “thread safety” within the code. Object creation also requires input confidence testing and object-oriented programming (OOP) testing due to encapsulation and polymorphism. Additionally, it is important to check any functionality that is above the base level (0 + 0). Testing is not required to cover box-code, MOC objects, or external code.

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Three Stages of TDD

TDD consists of three stages, namely “Red”, “Green” and “Refactoring”, and is based on several key principles. At the “Red” stage, a developer focuses on code logic visualization. For example, in the case of validation, it is necessary to envision the availability of the user, his credentials, and their validation. 

At the “Green” stage, you need to add the code and ensure its operation at a minimal cost. That is, one must at least add login and password fields when using the analogy of the user. At the same time, the use of only two fields will not allow increasing scalability of the project, which leads us to the third step. 

The “Refactoring” stage allows you to build an object initializer that will create further objects with the required data. Thus, before creating and implementing a project, it is important to test it.

Six steps for testing external code with TDD

If needed, a developer may validate external code using test-driven development in six steps:

1. Selection of the necessary functionality with the help of the facade pattern.
2. Wrapping the interface over the desired object and a third-party object.
3. Changing objects in parallel before they become similar.
4. Checking objects for equality using custom methods.
5. Using a proxy or dependency injection to switch between interfaces.
6. Testing the code that is written personally. 

The result should be an object that is to be tested but does not change the internal implementation of the third-party code.

TDD doesn’t exist without a “clean” approach because it minimizes the number of bug errors and duplicates. TDD involves moving in small steps and comparing the expected results with reality in the context of the “Red” > “Green” > “Refactoring” process. “Throws” error handling chains are among “Clean Code” practices. One may transition from one test to another only after receiving a positive result in “Refactoring”. By-products or methods at the “Green” > “Refactoring” stage may indicate which methods and qualities need to be encapsulated or removed completely.

TDD vs. traditional testing.

TDD guarantees that the project actually meets requirements defined for it. While traditional testing focuses on a test case design, TDD makes an emphasis on production code. Moreover, every line of code is tested, unlike after tests. Finally, TDD is more effective than traditional testing as this method involves testing logic at each stage of mobile application development. 

It is the efficiency of TDD that cuts its costs:

• This process decreases the time needed to launch and build the project, especially during cold starts;
• Tests change before changing the functionality which allows them to perform better;
• TDD brings down your stress levels;
• This approach supports the project legacy while simplifying writing tests;
• It is easier to study architecture in tests because they better indicate the ownership of objects;
• TDD its a part of software development automation 
• Finally, the code is cleaner.

Testing most of the functionality is possible with a single access point (CI). Each object method is called by setup and teardown. This approach allows you to change an object in just one test. It is crucial to test each case for errors.

Practical examples of TDD

This first example illustrates the creation of an object with user credentials (email and password). A red line appears to indicate that the code is trying to call data that does not exist.

In this case, a green line is achieved by entering the email and password in the hard code. This is the fastest way to get the necessary line color. Then, we run a test that indicates that everything is OK. But there is still a problem with a non-resizable form.

Thus, we add an initializer at the refactoring stage, which allows one to create several different users with various data. We check the refactoring again to obtain a green line.

In the second example, we create a validator for a user’s email. We write code and get a red line.

We create a validator for the green line, provide credentials, and validate email to track errors. We get a green line, but we have no description of the validation.

Hence, we refactor through the creation of enum which will act as an error. Next, we create a case and add logic to the validator. After refactoring, we get a green line.

TDD Summary

Test-driven development is effective and cost-saving. The ratio of code covered by tests in TDD can reach up to 60%. The three stages – “Red”, “Green” and “Refactoring” – are the basis for TDD. Its advantages include the unification of the process and reduction of errors in a project. In case of an error, it is possible to immediately contact the developer who is responsible for a particular part of the code.