Unit Testing vs TDD: An Easy-To-Understand Guide

Unit testing has been around for as long as there’s been programming.

However, the method has evolved over the years into something people call TDD or test driven development. TDD is all about writing the test code before writing the production code. This way, the developer knows what to code and what to test.

What’s the difference between unit testing and TDD? Unit testing is the art of creating automated tests for your code, usually after you have written the code. Test-driven development (TDD) is a set of practices where you write your unit tests before writing your production code and continuously run those tests as you write new code.

Unit testing focuses on unit functionality, while TDD also focuses on design and testability. However, with TDD, you also write unit test methods.

It’s difficult to say which is preferable. They each have their distinct advantages over traditional testing (manual testing, I’m looking at you). Here are some things you should know about unit testing and TDD before deciding which to use in your project.

What is unit testing?

Unit testing is a software testing process of checking small components of an extensive software system to make sure that they work correctly. It is the practice of isolating individual units using test doubles and testing that they function as required. Unit testing helps you to identify bugs and also helps you to correct them before any further development takes place.

Unit testing is essential because it saves time and money by avoiding expensive changes later in the development process. In addition, it ensures that new features will break the existing code. The developer typically does this process for every unit of code they create.

For the purposes of this post, when I mention unit testing, I am referring to the practice of writing a unit test after writing the production code. This approach is also called the test-last approach. TDD is also known as the test-first approach.

What is TDD?

Test-driven development (TDD) is an extreme programming process that involves a repetitive development cycle:

  1. Write a failing automated test case that represents the desired improvement or new feature.
  2. Write the minimal amount of code so that the new test and the rest of the test suite pass.
  3. Refactor the new code to acceptable standards. Refactoring is crucial for the overall code quality.

Because TDD emphasizes writing unit tests before any production code, it naturally assumes incremental development and design.

TDD is a good agile development practice because it forces programmers to think about what they need to do and why before coding. Thus, it ensures that programmers know what they want their code to do. It also helps them catch errors with existing tests before they slip to production.

Unit testing vs TDD – differences between the two processes

Unit testing is an automated testing process of checking the smallest parts of code to ensure that they are working correctly. Unit testing is done individually, which means that you write a unit test at any application development stage.

TDD is different in that it is a process of writing code to produce a testable design. This process includes writing both the code and tests for it at the same time. Furthermore, this process is done on a broader scale, which means that you repeat the TDD cycle several times before you get a working feature.

Unit testing is best for regression testing, while you can use TDD for new features. In addition, you can do unit testing quickly, while TDD takes more time because it requires some planning. It’s also more likely that unit testing will prevent bugs, while TDD will reduce the possibility of introducing a bug into your codebase in the first place. That’s because TDD naturally leads to better code design.

The purpose of the TDD is not to replace the “classic” approach of testing-last development. This is not because TDD has some inherent, fundamental flaw. Instead, TDD takes time for you to get used to this way of developing code.

If you are still learning how to write good tests, don’t worry about when you should integrate them into your overall development process. Instead, write good tests and worry about integrating TDD with your “classic” approach when you have more experience.

When to use TDD instead of unit testing?

Unit testing and TDD both help reduce the number of bugs in your code.

TDD is a design process that helps you to achieve clean code that has high code quality. It’s a good idea to use TDD when you’re coding a new project. On the other hand, unit testing is ideal when you have an existing codebase that you need to test.

Unit testing is more of a passive form of testing because it doesn’t actively modify the code to see if it works.

On the other hand, TDD is an iterative process where an automated test is written, followed by the code that will make the test pass. Once the test fails, developers make changes to the code to make it pass. TDD is more of an active form of testing because it actively makes changes to the code. Therefore, it’s best used during the early stages of development before adding features to your software.

TDD is an ideal approach for developers who are already experienced with unit testing. The process it utilizes is systematic and linear, meaning that it’s easy to follow. It also leads to high code coverage.

When to use unit testing instead of TDD?

There are some situations when unit tests are better than TDD.

When the existing code is complex, you cannot always write a unit test fast. If you can’t do it, don’t try to do TDD.

Instead, use mocking frameworks to provide stub and mock objects for the class under test and write the test method. Once you refactor the code a little bit and the unit test writing doesn’t take too much time, use TDD at that point.

Don’t worry about covering 100% of your code with unit tests – it’s not worth the effort. Especially if your codebase is huge – there is no way you can test every line of code. It doesn’t matter how much test coverage you have. The whole point of unit testing is to catch bugs before they ship, which is done by running unit tests often.

If your tests take a long time to run, you will avoid running them as often as you should and thus provide a false sense of security.


Unit testing is a process that breaks down your code into smaller parts, which makes it easier to test. Although it takes time to conduct unit testing, it can save you time later on if you find an error.

TDD, on the other hand, is a practice where you write tests before writing your code. This ensures that your code won’t break, and you’ll be able to make changes without worrying about the consequences.

This article has outlined the key differences between unit testing and TDD and helped you decide which will work best for your project.

Now, you can make a well-informed decision and start using these automation testing approaches in your project.

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