Test Driven Development: Your Best Friend For Designing Software

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Emil Krzaczyński

Jan 26, 2023 • 9 min read
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Do you focus on creating unit test cases before software is fully developed? If you don’t, then you definitely should.

Unit tests are the cornerstone of Test Driven Development (TDD). Investing in this process can provide immense value to your software design and development. Integrating unit tests into development results in increased code quality while decreasing development time, making TDD an invaluable tool for any product development team looking to maximize efficiency.

Leveraging usability and reliability principles to solve complex design hurdles

When you’re designing a project, new requirements get added on to the initial specifications all the time. If you want to build a useful, reliable piece of software, you need to make sure that it’s usable and reliable.

Usability is a basic software development principle that proves its functionality in the real world. You could do so through determining the goals of your software, concretely identify metrics for success, and set up a system that will grade your production code according to unit tests that validate the code’s functionality.

Reliability, on the other hand, is the principle that simply states that your production code should work as intended. Your code should simply operate failure-free.

Test driven development for designing software

TDD provides developers with the opportunity to rapidly move their production code forward. By introducing new requirements and thinking of use cases before implementing changes, they can easily create unit test cases that will help them identify any potential issues early on in order to prevent costly delays or revisions later down the line.

To define quickly, test driven development is a software development approach and one of the many tenets of extreme programming and agile development. The approach is “test-driven”, meaning that the technique’s primary intention is to modify or write new code only if it fails the test process.

Unit tests, therefore, should cover many, if not all, of the project’s use cases and specifications. Automated tests represent real-world scenarios and are used to prove the value and utility of your program.

In implementing test driven development that outline unit tests for each project specification, we ensure the usability and reliability of our software

The TDD cycle

The test driven development process can be done in three steps:

three steps of the test driven development process

Source: Impact QA

Writing the test

Writing a failing test is the first step of the test-driven development process. Seeing a test fail is vital as it proves that the newly added specification, in this case, the new test, is meaningful and unique.

The implemented code is proven necessary if the test was purposeful. When writing tests, keep in mind your project's specifications and requirements. The unit tests created should present different business situations that your software will be used in.

Without these tests, you’ll likely be haphazardly coding based on the hope that something kind of meets your requirements. They keep you on track and set the bar high for your build.

You may start by writing integration tests for your project.These are the instances that check specific interactions within the software. Examples of integration tests include payment methods, adding an item to a shopping cart, and package tracking.

Testing code

After listing down your test cases, now is the time to write code to make your program past the test. Because you’ve written your unit test beforehand, you have a rough idea of what you want to include and this improves your code quality.

Make it a point to write just enough code to pass one unit test. We want to emphasize that you should look to solve only one test at a time. That way, you correctly identify the goal and efficiently work towards a solution. Assuming you’ve written good test cases that meet your project's needs, then this iterative code testing process will speed up your development time.


You’ve run your unit tests and fortunately, it has passed. Now, your next step as the developer is to improve the structure. In refactoring code, we find the functional parts of the old code and the new solution. We aggregate these aspects together to come up with clean, well-structured code.

The TDD process is that simple – but how can this approach help us with the overall design? The process works as follows: by writing a unit test to add new features to the codebase, we can verify our design almost right away. If we mock the classes while writing tests, we can see the coupling issues and problems before writing code. The quick turnaround time saves the development team time and manpower.

How can TDD save money and time?

A key process of test driven development is to write tests that you’re sure your program will fail. The tests should cover business cases that our application is intended to solve.

In creating a failing test, the development team is forced to change how they think about the problem before they write code. Writing a failing test helps us understand the new requirements that we are to implement, and not come up with the most straightforward solution. A failing test case forces us to take a step back and reconsider the code we are really looking to implement.

As a business, one could easily see the value of this process.

First off, it saves money. In developing a program, how many times have you implemented a feature that you thought your customers would want – but as it turns out, the developers totally misunderstood the presented requirements.

A well-implemented TDD solves this issue by presenting a testing framework that your feature should pass. For example, test cases for a payment processor could outline the payment pathing as presented by the stakeholders.

Another advantage for TDD is that it “forces” us to cover more ground during the testing phase. A more intensive test suite means greater certainty that our solution should work and that future changes we’re looking to implement won’t break anything else.

Expandability is one of the most important things to consider when designing a system. This system's design principle provides for future growth and represents the ability to extend a system and the level of effort required to implement changes and improvements.

Finally, as an extreme programming principle, test driven development speeds up the design and release process. The factor to consider here is the time taken to get a feature to an acceptable, usable, and most importantly, releasable state.

The TDD process ensures the quality and reduces the rework, refactoring, or bug fixing effort in actually reaching a usable product. By defining our requirements and acceptance tests well before we write production code, the development time needed to achieve a releasable product gets cut down in half. It’s much easier to refactor code when you have substantial test coverage that helps you locate bugs in a codebase.

Does this improve the design itself?

Staying within the budget and on schedule are important project management principles. That said, these factors don’t directly improve the program you’re looking to develop.In this section, we answer the question: does test driven design improve the overall software?

There is a rule of thumb in software engineering that good code should be testable. While everything can be theoretically mocked, a test-first development process may lead to a false-positive. In other words, the code may be written specifically to pass tests and not to meet user requirements. Anyone who blindly trusts TDD would argue that if a program were to pass all the tests, then it meets all specifications.

This, unfortunately, is not true. TDD should be treated as a means to an end, it should be treated as a tool that implements unit test cases to improve code functionality. Remember that unit tests are never wholly equal to specification – focus on correctness and real-world utility when programming, not just passing tests.

That said, TDD, as a tool, creates better software through essentially a self-checking mechanism. As the code gets put through different testing frameworks, the codebase becomes more stable given the variety of situations it gets put through.

Introducing TDD in your software development project

It’s important to know when test driven development will and won’t work for your company or project. If you have a more complex application, this process can save you time and money by showing potential problems in the design before full implementation. However, for CRUD applications or other programs that are straightforward in nature, using TDD may be overkill. When deciding whether or not to use this method, consider the size and complexity of your software development project.

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Emil Krzaczyński

Python Developer at Netguru

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