Developers write tests to ensure that the software works as expected. They check for specific values, compare input to output, and look for errors.
But what if your tests could do more than ensure that the program is working correctly?
What if they could also guide your development process? These types of tests are known as test-driven development (TDD).
If you’re currently using TDD or would like to start using it, here are some best practices you should know about:
- Focus on one feature at a time
- Make sure each test fails initially
- Write a test before writing production code
- Have a good naming convention
- Write independent tests
- Automate tests
- Tests should execute fast
- Write short tests
- Use mocks to reduce coupling
- Refactor often
- Know when to use TDD
Tests are a great way to ensure that you’re not breaking things when you make changes. But what if your tests are broken?
In this post, I’ll show you how to write tests to avoid the most common issues.
What is TDD, and how can it help?
TDD is short for test driven development which can help reduce the amount of time it takes to develop software. It is a popular choice for large and small companies across the world. TDD is an agile, incremental approach for designing and building software using very short development cycles. Each TDD cycle goes like this:
- Begin with writing a failing test for the functionality that you want to implement.
- Then, write the new code to implement the functionality and make sure all tests pass after your changes.
- The last step is the refactor phase. In this phase, you eliminate duplication in the new code and make it clean.
As a developer, you develop software that is going to be validated against quality standards. You can meet this goal through test-driven development. TDD approach helps developers spot errors quickly when building systems and allows them to create the system without fear. You can also use the tests to verify that the code is still working and can be an example to show other developers how to use the system.
But, like anything else, you need to follow the best practice to get the most out of TDD.
1. Focus on one feature at a time
When following a test driven development process, focus on one feature at a time. This process is designed to be iterative and precise. Before writing any code, you need to write a test for the feature in question and define the expected outcome. Then, once you implement the feature, run the tests again to ensure it is working as expected. You can use this process for both big and small features.
When you work on one feature at a time, it is necessary to break that feature down into smaller sections that are easy to tackle. That will keep you more focused and more productive.
2. Make sure each test fails initially
For a test to be considered “good”, it should always fail before being fixed.
Why? Well, that’s because if a test initially fails, it means something is missing in your code. And after adding the necessary changes, the test passes. With this, you have also verified that the test covers that part of the code. So now, the green test shows an improvement in your code’s design or structure. Plus, you will probably get a small dose of dopamine after knowing that you are on the right track.
3. Write a test before writing production code
Test-driven development, while a bit unusual at first, is a great way to promote clean code by enforcing the idea of writing a test case before writing code. As a result, it will be easier to maintain the code in the future. And there is less chance that the code base will turn into legacy code.
Therefore, the first thing a programmer does in test-driven development is to write a test. This test provides all the requirements for the code.
When you write your tests after you have written the production code, the tests can’t help in designing the code. You also lose that extra step of checking that the test covers the code correctly.
4. Have a good naming convention
To do the best possible work, professionals must have a naming convention. A good naming convention saves time and energy for the developer and is helpful to the future developers who will come to maintain the code.
A good naming convention should be consistent and understandable to all developers working on the project.
When you run your tests, and some fail, the names help you determine what is going on. If your naming convention has unclear names, it may confuse you. You then have to go to every failing test, read the test code, and spend some time debugging it and the production code it covers. And all of that because you don’t understand the test’s intent.
5. Write independent tests
Unit testing is often considered the backbone of modern quality software development. This is because they focus on a single individual component of an application and are responsible for testing that particular component.
Unit tests are most valuable when they don’t depend on each other. If a test method depends on another unit test method, then the unit test fails if that other unit test fails.
What’s the reason one unit test depends on another? There might be several reasons, but the most common is when a test needs a proper initialization of an object, and the other test usually sets it up. When they execute in the correct order, everything is fine. But when you reverse the order or just run the dependent test in isolation, you get a failure. The best way to prevent this is to make sure every test sets up everything in its arrange phase.
6. Automate tests
Test automation can be a great way to get the most value out of them.
Automating the test execution is essential to ensure that your code is stable, fast, and scalable. The first benefit of automating the execution of tests is that it can save time. Once the test cases are automated, the tests can be re-run continuously. This is an excellent way to know that your code is still working and that no new regressions have been introduced.
The other benefit is that it will increase your confidence in improving the code. When you have a continuous integration system that will execute all unit tests, you have a safety net.
7. Tests should execute fast
When it takes longer than a minute to run your entire test suite, developers start running them less often. But without running the test suite, there is no way to know when the code breaks without someone finding it through manual testing or when the end-user sees it. Therefore, tests must run quickly so that people don’t neglect them due to the time it takes to run.
One of the benefits of unit tests is to quickly iterate on preventing errors and finding bugs in your code. If you’re able to iterate rapidly, that means you can also find errors more quickly. Test speeds can be a huge factor in this and are worth exploring further.
In general, the longer a test takes to complete, the longer it takes to iterate on it.
It’s vital to identify and eliminate reasons for slow tests. Unit tests should aim to be fast to fulfill their role. If a test takes too long to complete, it’s not possible to run it as frequently as it should be.
8. Write short tests
To create good, reliable software, you need to develop tests that are both rigorous and thorough. A unit test should be focused on just one part of the program and should be short enough to be readable.
Writing short tests is a great way to get instant feedback. When you can write a short test, that means that you can spend more time implementing the feature and refactoring the code. When tests are long, that usually means some of the following things:
- class is difficult to set up and has many dependencies
- test tries to cover more than one scenario
- there are parts of the test code that can be extracted and reused
All of the above are code smells and you should investigate and eliminate them.
9. Use test doubles to reduce coupling
The more time you spend on software testing, the more time you’ll save debugging later. But what if writing tests becomes difficult or slows down your coding process? That’s where test doubles come in handy.
A test double is a fake object that stands in for one of the real objects in the code. By creating mock objects, the tester can control what’s being tested more easily than using a live object. A fake database would be an example of a test double since you can’t test anything without data.
By using test doubles, you can only test one unit at a time instead of interacting with all parts of the system at once. As a result, you can write your tests faster and create less coupling in your code.
10. Refactor often
One mistake that even veteran developers make is that they never refactor code. Refactoring the code is essential for productivity, and by taking advantage of this, the developer can improve the quality of the code through optimizations. What does it mean when I say “refactoring” code? When developers refactor code, they analyze the code and rewrite it, often improving upon it.
While it’s not always easy to find time for this, refactoring can make your code more readable and easier to test later. When you think about it, refactoring doesn’t take much time. The trick is to make sure you do it often enough.
11. Know when to use TDD
Some companies believe that you should always use TDD and use it to achieve 100% test coverage. However, TDD is one of the many tools at your disposal when developing software applications. As with any other tool, there are times when you should use it, but there is also the time when you don’t have to use it.
For example, if you have a project with many dependencies and a tight deadline, your team would need to spend a lot of time trying to enable the existing code to write unit tests.
The other times when TDD doesn’t make too much sense when you do database changes or changes to the UI design.
In conclusion, test-driven development helps create a solid base for the complex systems being developed nowadays.
Many of the practices listed above will lead to improvement in your TDD and code quality efforts. While none of them are will make you TDD master overnight, the odds are good that many of these practices will help you write better and more maintainable code.