Test-driven development (TDD): the role of test-driven development in agile development projects
The evolution of agile development has created a number of pragmatic practices to deliver quality software quickly. Test-driven development (TDD) is now a recognised, effective approach that delivers positive results. It is a process where test cases are written first, followed by coding. In this article, we'll look at what you need to know about test-driven development, its benefits and pitfalls, and why it's important in agile projects.
What is test-driven development (TDD)?
Test-driven development (TDD) is a software development practice that focuses on writing tests before writing the actual code. In TDD, developers create small test cases for each feature based on their initial understanding. The primary goal is to modify or write new code only if the tests fail. This avoids duplication of test scripts.
The TDD approach stems from the principles of the Agile Manifesto and extreme programming. As the name suggests, the testing process drives the software development itself.
The place of test-driven development in agile development projects
Feedback plays a very important role in agile development. There is a high probability that project requirements will change during the development sprint cycle. To manage this, and to build products that adapt to the changing requirements of the customer, teams need continuous feedback to ensure that they do not end up with unusable software. TDD is built to provide such feedback early on.
Thanks to the body-first approach:
- Critical bottlenecks that hinder software quality and delivery can be reduced.
- Based on continuous feedback, bug fixes and the addition of new features, the system evolves so that everything works as intended.
- Improved collaboration between both the development and quality assurance team members and the customer.
- Since tests are prepared in advance, teams do not need to spend time re-creating extensive test scripts.
What is the difference between test-driven development (TDD) and traditional testing?
Now let's see how test-driven development is different and revolutionary!
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TDD is an agile development methodology where tests are written before the code is developed. In contrast, traditional testing takes place after the code is written.
Scope of testing
TDD focuses on testing small units of code at a time, while traditional testing focuses on the system as a whole, including integration, functional and acceptance testing.
Iterative
Test-driven development follows an iterative process in which small pieces of code are developed, tested and refined until they pass all the tests. The code is usually tested once and then refined based on the results of the traditional test.
Troubleshooting
The aim of test-driven development is to detect bugs as early as possible in the development process, making it easier to find and fix them. Traditional testing may require more effort to find bugs discovered later in the development process.
Documentation
TDD documentation typically focuses on test cases and their results, while traditional testing may include more detailed information about the process, test environment and system under test.
The benefits of test-driven development (TDD)
Now let's look at why test-driven development is good!
- Facilitates the creation of optimised code.
- A significant reduction in failure rates is observed, which is only associated with a moderate increase in initial development effort.
- It supports developers to be able to better analyse and understand customer requirements and to clarify requests when they are not properly defined.
- Adding and testing new features becomes much easier in later stages of development.
- Test coverage under TDD is much higher than under traditional development models. TDD focuses on creating tests of individual functions from the outset.
- It increases developer productivity and allows for a flexible, easily maintainable code base.
What are the pitfalls of TDD?
Typical individual errors include:
- forgetting to run tests frequently
- writing too many tests at once
- writing tests that are too big
- writing overly trivial tests, such as omitting statements
- writing tests for trivial code
What are the potential pitfalls at team level?
- partial acceptance, i.e. only a few developers in the team use TDD
- poor maintenance of the test set, causing it to run for too long
- rarely or never run a test suite due to poor maintenance or team turnover
The stages of test-driven development
1. Create accurate tests
Developers need to create accurate unit tests to verify the functionality of each feature. They need to ensure that the test is compilable so that it can be implemented. In most cases, the test is bound to fail. This is a telling failure because developers create compact tests based on their assumptions about the behavior of the function.
2. Correcting the code
If a test fails, developers must make the minimum changes necessary to update the code so that it will run successfully when re-run.
3. Revise the code
Once the test has run successfully, redundancy or possible optimisation of the code should be checked to improve overall performance. Make sure that refactoring does not affect the external behaviour of the program.
Best practices in test-driven development (TDD)
Finally, here are a few important factors to consider during TDD!
- Always start the process with an understanding of the requirements or specifications of the function to be developed - This will help to ensure that the tests are focused and relevant.
- Each test should focus on a specific behaviour or function - Tests should be small and focused, targeting a single aspect of the code. This improves the readability and maintainability of tests and makes debugging easier.
- Let's start by writing the simplest possible test that will fail - This helps us to focus on the task at hand and avoid having to deal with more complex issues.
- When designing tests, take extreme cases into account - These are important because they can often reveal potential errors or unexpected behaviour.
- Once a test has been successful, it is important to take the time to refactor the code and improve the design without changing its behaviour - this will help maintain clean and maintainable code as the project progresses.
- Always have fast feedback - This allows for faster iterations of development and early detection of problems.
- It is worth using test automation frameworks and tools to automate the execution of tests - This enables frequent test runs, easy integration into the development workflow and consistent and reliable test results.
- Compliance with the basic TDD cycle - Write a failed test, implement the minimum code to pass the test, and then refactor the code to improve the design. Then repeat this cycle for each new behaviour or function!
- There should be an appropriate balance between unit tests, integration tests and acceptance tests - Each test type serves a different purpose and provides different levels of confidence in the code.
- Testing failures should drive development - If a test fails, it should guide development efforts. Analyze the error, identify the cause, and improve the code to fix the problem. Test failures provide valuable feedback to improve the quality of your code.
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