Programmers write thousands of lines of code a week, or even in a day. According to the book Code Complete, 1,000 lines of code contains an average of 15-50 bugs (errors, typos, or just things that don’t work). This can result in hundreds of hours that developers use to fix the problems.

Even when the code does not contain errors, sometimes the programming does not achieve the intended goal. Determining why and how to fix it is often a complicated procedure. The software development process is made more efficient by using test-driven design.

A Brief Explanation of Test-Driven Design

Test-driven design or test-driven development (TDD) is a cycle of programming and tests that is followed by reworking. Programmers determine the goal of the code and set up the test. If the test fails (which it always should the first time), code is added to make it work. The programmer strives to minimize the number of lines of code. As a result, they add new lines little-by-little to keep it simple.

This method allows programmers to limit or remove duplication in the code, arrange code logically, and see immediately if new code breaks the program. The tests themselves are named in such a way that they explain what they are written to test.

Some call this system Test First Development. Each test case is set up to define what needs to happen, and the tests determine if the code is properly created and organized. The creation and reorganizing part of this process is known as refactoring.

Tests of the program are run every time new code is added or changed to make sure they continue to succeed. If a test that previously succeeded fails, then the developer knows that the new code has a problem. Using TDD means that only a small amount of code needs to be changed when an error occurs. When all tests succeed, the developer adds a new test, beginning the cycle again.

Terminology aside, test-driven design is less about testing and more about building a set of specifications that propel development. Testing is, of course, an integral part of this. But the goal is not to test or to pass a test but rather to create a usable, functional program.

1. Test-Driven Development Offers Key Benefits

The main benefit of test-driven development is the confidence that programmers establish and foster by adjusting programs to add functionality. Rather than adding new snippets to the end of the file (which limits integration), the TDD method integrates the code in each cycle, which results in programs that work efficiently no matter when new functionality is added.

The ensuing programs after completing this process tend to be higher quality products that contain fewer bugs and cost less due to increased productivity. The time it takes to get the programs finished and ready to market is much shorter. Because the tests double as examples of how the code works, they can be used to document the project for other developers or end users.

The code developers create using test-driven design is easy to maintain, change, and extend. The code is solid, simple, and focused because developers write it to pass a predetermined test. Debugging and finding problems are much more straightforward since feedback is much quicker. All of these factors combined allow programmers to reduce reworking time dramatically.

Because the test case is a needed function or component of the program, writing the tests for this process depends on the developer’s knowledge of the desired program. The entire process is much more deliberate and precise as a result, which aids in creating clean, concise code. While entirely preventing defects is virtually impossible, detection occurs much sooner through TDD implementation.

If the programmer’s understanding of the program changes, the design can easily grow and change in tandem with testing. This flexibility is due to the modular fashion in which the design is developed. Development in chunks or units makes the whole program much cleaner and cohesive.

The TDD method overall prevents typographical errors or other defects occurring from injection, whether due to small changes and fixes done without testing. The regular, consistent verification of the code’s integrity draws attention to issues quickly, allowing the developers to correct them immediately.

2. Test-Driven Design Uses Small Steps

The advantage of using small steps when creating a program is that a programmer can undo a discovered error with an accompanying small step. Finding typos or missing characters is much easier when there are fewer characters to check as well.

For example, consider a program that passes all the tests thus far. A programmer adds a new test. When testing the new code, a previous test fails. Only the new code needs adjustment from there, since the code has already been tested and previously passed successfully. A single undo returns the code to its working status. The code snippet can then be examined and adjusted, or rewritten to better fill in its segment.

3. Test-Driven Development Provides Faster Development

Because each unit, step, class, variable, etc., is created to meet predefined requirements, overall programming speed can be faster than when using other processes. It produces simple, concise code sufficient for the test case, which generally takes less time to write.

Developers who are inexperienced in test-driven development may feel that writing code using TDD takes more time. According to a study, work time usually increases by 15-35% using this method. The same study shows that the pre-release defect density decreases by 40-90% with this process. Since rework time can take up to 1500 hours when not using TDD, the initial time investment suitably offsets potential rework time and often reduces the overall time necessary for the project.

The notable increase in speed is more recognizable when the programmers get to the last steps before product release. With traditional programming, if an error appears at this point, it can set the whole project back to step one. With TDD, the error becomes apparent shortly after its inclusion. When the program is nearing release, any defect that turns up will be identified only for the current unit rather than the whole program.

The process is also faster because automated testing is possible. While manual testing still has its place, faster automated testing improves the time of the process and the finished quality.

4. Test-Driven Design Overcomes Inherent Testing Problems

Standard testing methods are more difficult due to potentially inherent problems. The test-driven development process handles most of the problems quite efficiently.

Inadequate Testing Schedule

In many software development situations, the testing proceeds after a large quantity of code is completed. This makes it hard to track down the cause of failure.

With TDD, each module is created explicitly to make its test succeed. Every unit is tested both before and after its creation. This consistent testing keeps all the code checked and accurate throughout the development process.

Lacking a Test Plan

Without a plan, tests may be run inconsistently and miss defects. Because units are written based on tests with TDD, the test plan is an integral part of the process. Developers are required to run the tests on schedule to continue the code.

“One Size Fits All” Testing

Even clothing manufacturers now admit that one size only fits most. When the developers don’t consider the unique requirements of a program when setting up tests, the results may be insufficient. With test-driven development, testing universally is not possible. A programmer drafts each test case for an exact program and an express portion of code to be most effective.

Requirements are Unclear

The possibility of tests being deficient due to an incomplete understanding of the requirements is much higher in standard testing. Since the whole point of test-driven development is to create clean code that does a specific task or provides a distinct bit of data, the requirements are always right in front of the programmer in the form of the test case. The test defines the requirements.

Test Communication is Inadequate

Documentation of tests and the information is not consistently updated within standard testing conditions. Test-driven design uses the test cases as documentation, which means that it is always up to date and clearly delineated.

Testing if the Software Works

Sometimes programmers perform tests to determine if the program operates after finishing the first draft of code. In this scenario, they may overlook any defects in the program if they find that it completes its intended functionality. However, key errors may still exist that will pose problems down the line. 

By using test-driven development, they can find any errors in the code immediately rather than when they finish the program.

Unclear Testing Requirements

When requirements are questionable, lacking, partial, imprecise, or erratic, further derived requirements may be completely incorrect. Verification will be unclear, and responses will be dubious. Test-driven development uses specific requirements that are laid out and precise.

5. Test-Driven Development Results in Looser Coupling

Coupling refers to the interdependence between modules. The fewer connections, the more flexible the modules are within the program. Too many connections between units can cause problems in later testing and make singular testing very difficult. Loose coupling provides code that is convenient to customize over time.


By engaging in test-driven development, you can significantly reduce the number of defects in your code. This technique ensures a simple, readable, decoupled, and changeable code that will work from the get-go, so you can get it to market sooner.