What Is TDD? Test Driven Development | Know It All

TDD (Test Driven Development)

What Is Test Driven Development (TDD)?

Test Driven Development (TDD) is like the trial and error method in agile software development process as well as in testing. And, that makes it a widely accepted approach for developing apps and performing tests efficiently. It is the method of developing the tests even before writing the code that validates them. In layman’s language, the approach in which tests are created to check a functionality, they are run, and when they fail, the code is rewritten to pass those tests. This may sound complex and tricky but following this approach leads to having simpler and bug-free code.

During the initial phase of this amazing software engineering practice, tests (mostly unit tests) are designed and developed to check if every functionality of the application is working properly. Then comes the waiting phase for the tests to fail so that new code can be written to pass the tests and eventually, lead to an efficient codebase

The primary agenda of TDD is correcting the failed tests before proceeding with new development works. This approach comes with the advantage that as you need to pass the tests only, you have to write a small amount of code at a time or just refactor code, and can easily avoid duplication. Due to this method of creating and running automated tests even before the beginning of the actual development phase, this approach is also called Test First Development. We would suggest that if you are a fan of using the trial and error method then go on with every part of this article, get to know everything about TDD, find out all the suitable situations to apply it, and proceed with using it.

Advantages of Test Driven Development

Though we guess that the definition part of TDD is good enough to make you a fan of it, you must know about its amazing benefits to bring it into practice immediately. So, let’s check them out.

Earlier and Easier Bug Detection

  • For a long, the traditional method of detecting bugs has been mostly executing tests manually. As that method commonly consists of executing test scripts one-by-one and the testers need to analyze the faults by themselves, eventually, the process would become extremely time and resource-consuming. On the other hand, TDD process enables you to create efficient automated test suites that you or any other member of your team can run whenever required.

Better Understanding of The Objectives For More Efficient Code

  • TDD encourages and helps the development team to have an in-depth understanding of the clients’ requirements as well as of the user stories. And, if you do not have that, it will follow an approach of requesting better clarity.
  • When you know everything about the goal and use cases of an application, you become able to make a better plan about how different functionalities of the application should interact with each other and how they should perform.
  • In-depth planning helps you to build a more efficient design and a codebase with enough code that can do the job while you can easily maintain them.
  • As the primary style of writing code in TDD is writing small codes for single responsibilities rather than following monolithic procedures with multiple responsibilities, the code eventually turns out to be simpler.
  • As TDD is only concerned about passing the tests, following this approach exempts you from the headache of writing different sets of code other than production code.

Better Balance In The CI/CD Pipeline

  • Often, it becomes necessary to add some features to the application at some later stages of the development phase. And, no feature can be passed without testing them properly. TDD lets you get rid of that stress and you can add any feature at any point of the development cycle. So, eventually, you become able to maintain a stable continuous integration and continuous delivery process.
  • Due to different situations, you may have to refactor your code. In usual methods, such code refactors cause the code to break. But, as TDD primarily focuses on a single factor that the tests pass without any hassle, it becomes easy for you to get rid of the possibilities of such breaks through automated tests before the app is released. You get a proper warning when such a break is found so your task becomes easier.
  • TDD leads you to have faster and more efficient code that has very less risk for bugs and can be easily updated.

Better Test Coverage

  • If you wanna know about the importance of test coverage, ask that company that is struggling with numerous apps or functions that are never performing properly. To cope with the enormous growth in the number of users and their demand in the modern tech world, companies are somehow being forced by the market’s pressure to keep on launching new products with numerous features. In such a scenario, those products need to be tested as soon as possible.
    As TDD prioritizes passing the tests first and keeps the code really simple, you get the opportunity to execute more tests in less time, and eventually, you proceed towards greater test coverage.

Improves Teamwork

  • TDD works with the simple objective of developing anything in a way so that the already created test cases pass easily. As we previously mentioned, such a simple trial and error approach helps you keep the codebase simpler. Hence, the simple motive of anyhow passing the tests enables any member of the team to successfully complete the testing process while the members who are responsible for the tests are absent.
    Also, such collaborative teamwork enhances the knowledge of the whole team and eventually improves their overall work efficiency.

Makes The Job Easy For The Developers

  • Writing the test cases for TDD may consume some time but the simple objective of somehow passing those tests makes it a lot easier for the developers to direct their focus on developing and debugging new features. As a result, the application gets built on a simple and much more efficient codebase.

Disadvantages of TDD

Like every creation of technology, TDD also has some disadvantages. Check them out below to make your strategies in a way that the disadvantages do not bother you much.

Requirement of Remarkable Skills

  • TDD is popular for its benefits in favor of a tech business but if it requires an unimaginably high level of knowledge and skills, you will be restricted from adding many members to the respective team. And, this happens with TDD on a significant level. TDD requires the respective persons or the team to be highly skilled. The issue mostly occurs during the unit testing phase in TDD. For performing unit tests in TDD, each and every component needs to be absolutely isolated but many legacy systems are often not built in that way.

Often Becomes Time-consuming

  • As you saw in the previous point, to become successful in TDD, your team needs to have immense skills. To avoid being out of date, every member of the team must be capable of creating and maintaining the unit tests. For all these learnings and the lengthy initial planning of TDD, it becomes initially time-consuming so that you can achieve a greater pace later.

They Are Not Full Proof

  • Even after such immense hassle to follow TDD efficiently, it does not become an absolute thing that the results will be the best. Like every other popular test method, the final results in TDD also depend on factors such as how thoroughly they have been performed and how the end users mimic the conditions that they will encounter.

How To Perform TDD Tests?

Till now, you got to know what TDD is and why it is so advantageous. Now, you must be aware of the most efficient way to use it so that you can achieve the best results. Hence, let’s check out the step-by-step process.

Creation of Precise Tests

  • As we are talking about TDD, it goes without saying that the primary task is going to be creating specific tests to check every single feature. So, your role starts with creating very precise tests that ensure that all the functionalities of every feature are working properly. However, these tests are built with the motive that they have to fail in a way that clearly shows how that specific feature should perform.

Running The Tests and Waiting For Them To Fail

  • Now, as you have built the tests in a way that they will fail so now it’s time to run them and wait for them to fail. While creating them, you had the assumption about how the feature should ideally behave. Running the tests and their failure will depict the points where the functionalities are lagging behind.

Correcting The Code For Actual Development

  • The initial creation of tests was to find out the best way to develop the features. Now, it’s time to proceed with that. In the previous phase, you have figured out why the tests are failing. So, now go on with the later part of the trial and error method, and write the correct code to pass the tests.

Run The Tests Again and Refactor The Code

  • You have finished writing the correct code for the features so that must be verified by rerunning the tests that previously failed. Run those tests again, observe if the features are underperforming at some points, and notice those points that can be improved. Then refactor the code to improve the overall performance of the application. However, you must make sure that the tests are running successfully and that the code refactoring is not affecting the external behavior of the program.

Repeat The Whole Cycle

  • TDD is an approach where you work with one functionality at a time. So, you have to keep repeating the same test cycle until you ensure that every functionality and feature of the app is properly tested and improved for the best quality.

Key Factors of TDD Cycle

  • Write a test for a specific functionality.
  • Run it.
  • Let it fail and observe the cause of failure.
  • Write the actual code for the test to pass.
  • Run the test again.
  • Point out the scopes to improve the quality.
  • Refactor the code to improve the quality.
  • Repeat

Some Points To Keep In Mind About Test Driven Development

  • The objective of TDD is neither “testing” nor “designing”.
  • TDD does not depend on the motto that says to write some tests and then build a system to pass those tests.
  • TDD does not encourage you to do a lot of testing.

Difference Between TDD and Traditional Testing

We know that traditional testing has served the tech world for a long. So, why is TDD suddenly getting so much attention and preference? Well, the following differences between them can clearly explain that.

Traditional Testing

Test Driven Development (TDD)

It is mainly focused on testing. It tests your code after the development phase.

It is mainly a specification technique that thoroughly tests your code at the confirmatory level.

In this approach, you are looking for fewer bugs or faults so that your app can move to the production stage faster.

In this approach, you want the tests to fail so that you get the opportunity to write simpler and more efficient code for the functionalities.

Traditional testing helps you identify the faults in your app. The more faults you notice, the more you get worried about the quality.

TDD ensures that the features are working as they were planned. Failing here lets you make it even better and you get more confidence in your app.

Here, the focus is more on the test case design so that it clearly shows if the application properly runs to fulfill the requirements.

Here, the focus is more on the production code to ensure that testing works properly because the proper working of the tests will eventually ensure the best performance of the app.

Traditional testing can almost never achieve 100% test coverage.

As TDD is primarily focused on tests, it surely achieves 100% test coverage. You can stay relaxed as every single line of code is tested and improved for better performance.

If traditional testing is more prioritized, it establishes greater importance of testing.

If TDD is given more attention, it leads you towards building a perfect product.

In this approach, the purpose is pre-applied in the feature before testing.

In this approach, the purpose is applied after the test fails.

Acceptance TDD and Developer TDD

The two crucial levels of TDD are as follows-

Acceptance TDD (ATDD)

This is the method of writing a single acceptance test that is good enough to check the normal operation of any feature. In the next step, that acceptance test is fulfilled by writing some production/functionality codes. ATDD focuses on specifying detailed, executable requirements for your solution on a Just In Time (JIT) basis. Also, for its centered focus on the overall behavior of the system, it is also called Behavioral Driven Development (BDD).

Developer TDD

Similar to ATDD, Developer TDD is all about writing a single developer test that is a unit test and then moving on with writing some production code to fulfill that test. And, as we know, unit tests concentrate on ensuring that every smaller than the smallest software module/unit is performing properly. However, unlike ATDD, Developer TDD does not have any special name. It is simply called TDD.

Though ATDD and Developer TDD are two different levels of TDD, they work with the same objective which is specifying detailed, executable requirements for your solution on a Just In Time (JIT) basis. JIT eliminates the extra burden of taking unnecessary requirements into consideration and as a result, you get to experience a higher level of overall efficiency.

Scaling TDD via Agile Model Driven Development (AMDD)

Though TDD works like magic in specifying minute details and in different validations, it does not perform that great for checking larger things such as overall design, use of the system, or the UI. That’s where AMDD joins hands with TDD to scale it or improve its capabilities. Let’s check out how that happens.

The Lifecycle of AMDD

AMDD consists of a step-by-step step process that includes different stages with different durations. A list view of that process is shown below.

Iteration 0: Envisioning (Duration: Several days)


  • Identifying the high-level scope.
  • Identifying the initial “requirement stack”.
  • Identifying an architectural vision.

Iteration Modeling (Duration: Some hours)


  • Focusing on iteration planning.
  • Modeling enough to give good estimates.
  • Planning the work for the iteration.

Model Storming (Duration: Some minutes)


  • Working through specific issues in a JIT manner.
  • Figuring out the requirements in detail through the active participation of stakeholders.
  • Evolving requirements throughout the project.
  • Modeling only as much as needed for now. You can come back anytime later.

Test Driven Development


  • Developing a working software via a test-first approach.
  • Capturing details in the form of executable specifications.

One important characteristic of Agile development is that it needs regular feedback to develop the expected product. For this reason, Agile development is also called Feedback Driven Development.

Now, it’s time to break down the AMDD lifecycle and check them out in detail.

Iteration 0: Envisioning

This phase is further divided into two sub-phases that are described below.

  • Initial Requirements Envisioning: It is almost pointless to proceed without complete knowledge of the high-level requirements and scope of the system. So, this is the phase where you will spend several days analyzing the usage model, Initial domain model, and user interface model (UI).
  • Initial Architectural Envisioning: Identifying or deciding the architecture of the system and setting technical directions for the project is another task that also takes some more days. This is the phase where you need to concentrate on exploring technology diagrams, User Interface (UI) flow, domain models, and Change cases.

Iteration Modeling

As the name suggests, this is the phase where you need to plan and build a model of the work to be done for each iteration. Check out the activities performed during this phase in a list format below.

  • Using agile processes for each iteration is a common practice. That means during each iteration, you can and have to add a new work item.
  • Works are taken into consideration as per their priority order. Also, you have the freedom or flexibility to reprioritize the added work items or remove some from the items stack at any time.
  • Discussing and deciding the implementation procedure of each requirement is the prime activity that is performed in this phase. And, that is the modeling step, the defining step of this phase.
  • This is also the phase when you perform modeling analysis and design for each requirement that is going to be implemented for that iteration.

Model Storming

The proper modeling is already done in the previous phase. So, this is the phase where the model is analyzed and if necessary, some modifications are made just before the actual implementation of the model. Due to such instant remodeling steps, this phase is also called “Just in time Modeling”. Now, it’s time to break down this phase.

  • During this modeling phase, issues are discussed by 2-3 designated team members. They commonly use paper or whiteboard for better representation of their ideas.
  • As the team members involved in this phase work collaboratively, it eventually becomes a phase with a very short duration like approximately 5-10 minutes.
  • Every issue is analyzed until the root cause is identified. And, when it is detected, one team member gets on resolving it while taking help from the other ones.
  • Other team members then understand the problem before moving on as they were initially doing. For such activities occurring during this phase, it is also called stand-up modeling or customer-QA sessions.

Test Driven Development (TDD)

It’s great to see that the final phase of the AMDD lifecycle carries the name as our topic of all these discussions. So, let’s see what happens in the TDD phase.

  • This phase is concerned with confirmatory testing of your application code and detailed specification.
  • Acceptance tests (detailed requirements) and developer tests (unit tests) are used as inputs for TDD.
  • As you already know, one of the main objectives of TDD is to keep the code simpler and clearer. So, eventually, it enables the developers to deal with less documentation.


Though it is always a great practice to review your works, it can be categorized as an optional action. However, this phase has some specifications like -

  • Code inspections and model reviews are part of this phase. So, it can turn out to be helpful in receiving better results.
  • If you wish to get nearly perfect results, you can perform the review action for each iteration or once for the whole project.
  • We have seen how feedback is highly important for a successful project. Hence, reviews can be truly beneficial for receiving proper feedback.

Differences Between Test Driven Development (TDD) and Agile Model Driven Development (AMDD)

Previously, you saw how TDD can become more efficient and advantageous when it is scaled through AMDD. But, there are some differences between them that you must know to get the best out of it. Hence, let’s dive into the differences.

Test Driven Development (TDD)

Agile Model Driven Development (AMDD)

As TDD is based on analyzing the causes of every test failure, following this approach shortens the programming feedback loop.

As AMDD follows the method of building detailed models first, following this approach shortens the modeling feedback loop.

TDD concentrates on every small reason behind a test fail so, the focus remains more on detailed specification.

AMDD works with the objective of handling bigger issues.

With TDD, you can stay assured that your code is going to be simple, high quality, and has no duplication issues.

With AMDD, you can stay assured that your followed approach will ensure high-quality communication with stakeholders and developers.

TDD mainly deals with programmers.

AMDD mainly deals with stakeholders, business analysts, and data professionals.

TDD is non-visually oriented.

AMDD is visually oriented.

As TDD means just passing a test with some coding, it has very limited scope for software work.

As AMDD involves a lot of non-technical people who have a great understanding of the products in their journeys, it has a really broad scope.

Let’s Break Some Myths and Misconceptions About TDD

Test Driven Development is undoubtedly an efficient approach that helps you keep a simple and effective codebase, and leads you to achieve amazing results with strategized minimal efforts. But, similar to many advanced technologies and methods, there are some widely spread myths and misconceptions about TDD. Hence, we are providing you with the logical explanations that will demolish those misconceptions effectively.



TDD makes you build a 100% Regression Test Suite

Well, there is nothing wrong with creating a 100% Regression test suite. However, it is not a true fact either. Let’s see why -

  • The first fact revolves around testing some reusable components. Your app may have some reusable components/frameworks that come with neither the test suite nor the source code. You might have downloaded or purchased them. And, when you create some black-box tests for them, remember that those tests only deal with the interface of the component but do not validate the whole component.

  • Testing user interfaces with a dedicated focus is not a common action. People commonly do not have user interface testing tools or those are very difficult to use. Instead, they do not automate testing user interfaces and hope that their user testing efforts take care of those too.

  • The issues might not have been caused by TDD but by some developers on the team without proper skills.

  • 100% Regression test suite means Database Regression testing too. That is not only a new concept but also has a very little number of tools available that support it.

  • While working on a legacy system, it takes a bit of time and strategic efforts to write the code for testing a legacy functionality.

Your complete design specification is covered with unit tests

This misconception is commonly spread by people who never had any involvement with an actual agile project. In reality, unit tests are responsible for forming a bit of the design specification and the acceptance tests are responsible for forming a bit of your requirements specification. As we saw in the AMDD lifecycle, the modeling and documenting works are smartly done by agilists. As the working procedure in TDD makes you concerned about the production code before writing it, a detailed designing work is performed by you.

Unit tests become your only requirement

It might be true for the simplest systems but all other systems can never be tested based on this theory. The agile method will clearly state the need for all other testing techniques.

TDD is sufficient for the complete testing procedure

It is a terrible misconception. TDD is only good for unit/developer tests and at the customer test level. It is only a part of your overall testing efforts. Its maximum capabilities are around the confirmatory tests. But, as previously discussed, no matter how much TDD helps you, there remains a requirement of independent testing that has no involvement of TDD.

TDD does not scale

Though there is a partial reality to this statement, you can easily get over it. The most common scalability issues about TDD are as follows.

  • Long Running Times of Your Test Suite: This common issue can be easily solved with a simple strategy. To solve this problem, you need to separate your test suite first into two or more components. Now, while one out of them will contain the tests for the new functionality that you are currently working on, the other one will contain all other tests. The first suite needs to be run regularly and you have to keep migrating the older tests to the overall test suite. The overall test suite needs to be run in the background, often on a separate machine, and/or at night.
    However, depending on the load, availability, and hardware, different test suites like development sandbox tests, project integration tests, etc. can run for different durations ranging from some minutes to several hours or days (such long running test suites are very rare).

  • Developers’ Knowledge and Skills Play An Important Role: The backlash of your TDD approach may not be caused by some flaws in the method. The developers should have proper knowledge and skills to make the best out of this approach. Keep a check on them if they are not very likely to adopt TDD. If that is the case, make sure that they get proper training and make them collaborate with people with great unit testing skills.

  • The Whole Team May Not Be Following TDD: If you want to get results from following TDD, your whole team should follow the approach. If there are some people in the team not following it, you can choose any solution from below -

    • Make sure that they start using it.

    • They can move to any other team.

    • The whole team leaving TDD will also work.

Frameworks For Test Driven Development

TDD is a remarkably efficient approach for many programming languages. Hence, there are some popular frameworks that help you get the best results from TDD in any specific programming language. We are jotting them down below.

  • csUnit and NUnit – These are two open-source unit testing frameworks for .NET projects.
  • PyUnit and DocTest: This is a popular Unit testing framework for Python.
  • Junit: It is a renowned unit testing tool for Java.
  • TestNG: It is a popular Java testing framework that overcomes the limitations of Junit.
  • Rspec: It is a great testing framework for Ruby projects.


This article clearly shows how useful and advantageous TDD turns out to be. If you are looking for an efficient strategy for getting an awesome development experience, you can surely opt for TDD. Go through this article carefully and acknowledge yourself with everything you need to know for excelling in this approach. We have tried to cover every minute detail that can help you on your path to becoming a pro follower of Test Driven Development.

However, it goes without saying that if you want to stay away from the hassle of writing test codes and want your whole team to work collaboratively for testing your product, your only and most effective solution is using Preflight, one of the most renowned automated testing tools. This simple and magical browser extension can provide you with unimaginable software testing benefits. All you need to do is just book a demo.

For more information, our amazing website is always there to serve you. Also, you must keep abreast of the latest technical topics from our blog page.