Integrating TDD Into the Product Development Lifecycle

By Rahul Vala

September 17, 2025

All the technology products we use today, from mobile applications to connected cars and industrial controller systems, depend on software as the invisible backbone for functionality. Software is no longer simply a product component; it determines user experiences, produces business value, and provides competitive differentiation. With systems continuing to connect faster and become increasingly complex, the ease of assuring software quality continues to be one of the most difficult challenges in product development.

Conventional testing approaches, in which code is built and then tested, are becoming less reliable. They typically only identify bugs after a feature is completely developed, significantly increasing defect costs and the risk that defects will arise further.

This additional risk includes unrecovered bugs being unintentionally released into production, which could also lead to serious damage in terms of security, performance, and customer trust.

This is where Test-Driven Development (TDD) can be introduced. By testing, at the start, TDD allows development teams to develop and design for quality, from day one!

In this article, Rahul Vala, Senior Principal Engineer – Automation and QA, shares how TDD can enhance the testing of industrial automation, enhance confidence, agility, and resilience in every step of product development.

1. Should we write tests after the code is done (Script-Driven Development, or SDD), or should we write tests first, driving the design (Test-Driven Development, or TDD)?

Ans: There is still a continuous tussle on whether you should write your tests after you create the code (Script-Driven Development or SDD) or if you should write tests first and design the code around the tests (Test-Driven Development or TDD).

In many ways, SDD makes sense: we create the feature and then add in tests to verify it works. The downside, however, is that usually SDD provides weaker test coverage and ultimately results in code that is significantly more difficult to maintain.

Since the tests are created reactively after the code is written, most edge cases and unexpected behaviour will be overlooked, resulting in a reactive software quality assurance process. Problems are discovered typically much later in a project, often in production, and by then, it is typically much more costly to address.

TDD completely changes this process by starting with a failing test that defines what the code is intended to accomplish. The developer then just writes enough code to make the test pass and then returns to improve the code with the knowledge that will pass the test.

TDD promotes better design decisions, cleaner gives results in and more modular code, and creates more confidence with each code change. Over time, TDD reduces debugging attempts, avoids regression, and results in solid and maintainable software.

2. What can go wrong with traditional testing or the Script-Driven Development (SDD) approach?

Ans: Script-Driven Development (SDD) appears to be a reasonable approach at first glance: you write your code and then you write your tests afterwards. But SDD brings with it several hidden risks that can impact software quality and long-term maintainability.

A major issue is a delay in testing and feedback. Since tests are written after development, bugs and design flaws are often discovered late, making them hard and more expensive to fix. The initial stage mistakes that could usually be caught, usually slipped.

Another concern is poor test coverage. Because the test is not made in this process, developers can only test the “Happy Path”, which means they check that the software works in ideal conditions but ignore unusual or edge cases.

For example, a payment system can only be tested for successful transactions, but not for failures such as card or network errors. Over time, these interval makes the software delicate, and when the real-world condition is different from the ideal, there is a possibility of breaking.

SDD also produces designs that are tightly coupled and rigid. Without the guidance of tests on how the components are structured, we tend to develop codebases that become messier and are harder to refactor, and create technical debt.

Over time, the lack of structure will affect developer confidence. The team will be reluctant to make changes because they are concerned that making that change might simultaneously break something already working, which stagnates both innovation and delivery.

Finally, the cost to maintain the design increases. Without a strong base of tests, bug fixes, and enhancements will naturally reintroduce past bugs, which will leave the system brittle and unmanageable.

3. How does the Test-Driven Development (TDD) approach work, and what are its key steps?

Ans: Test-Driven Development (TDD) is an approach that creates tests first before writing the actual code. Instead of producing code and then checking if it meets the requirements later, TDD makes testing the driver of design. As a result, the software being developed is, from the start, closely aligned with the requirements and is also inherently reliable.

The first step is to translate requirements into small units that can be tested. Developers will create automated unit tests to specify what the system must do. For example, if a feature requires login validation, the first thing the developer can do is to test the behaviour of the system given valid or invalid credentials.

Then developers only write enough code to make that test pass, which emphasizes simplicity and clarity, except for any unnecessary logic or extreme cases. Once the test is passed, the developer will do the refactoring, which means that cleaning, adaptation, and documentation of the code for future maintenance, while not changing the actual behaviour of the code at this stage.

This process, known as Red-Green-Refactor, means you write a failing test first (red), you write just enough code to make it pass (green), and then rewrite it in a way that you are improving the code while not breaking the tests (refactor). If you repeat this for every feature, update, or bug fix, over time it leads to more stable code with good test coverage, fewer defects, and software that is easier to maintain and scale. In other words, TDD is not just about testing; it is about building quality into the development process.

4. How can TDD be integrated across different phases of the product development lifecycle?

Ans: Test-Driven Development (TDD) is most useful when implemented throughout the life cycle of the product. TDD is a ‘shift-left’ approach, where the tests are created earlier and run more often. This helps in tackling issues at an earlier stage before it helps evolve into unexpected problems in development.

During the Requirement phase, TDD entails teams working on test scenarios that match user expectations, such as end-to-end flows, regression tests, and acceptance criteria, so that we have a good understanding of what success looks like before we write the first line of code.

In the System Design phase, TDD can also be used to identify integration points early, supporting database tests, API tests, and mocking of external services as part of the design, alongside running CI/CD pipelines that validate every build, so they aren’t compromised.

TDD Integration with various phases of Product Development Lifecycle

The Coding phase is where TDD shines. Developers first produce unit tests, then the code, and finally, they will refactor the code with confidence, with automated checks to enforce coding standards, measure coverage, and detect regressions to code changes immediately.

By the time we reach the Deployment phase, TDD also adds value with automated smoke tests, checks for system health, and deploys the application in a safe, repeatable process.

Using the TDD toolchain/support frameworks, Pytest, Selenium, Jenkins, GitLab CI, SAST, and coverage analysers, TDD is a lifecycle practice that introduces defects early in the process, provides back-to-back feedback, and better overall products that are maintainable and dependable.

5. How can development and test automation sprints be aligned using TDD to achieve continuous quality and faster delivery?

Ans: Test-Driven Development (TDD) provides a straightforward approach to managing development and testing automation sprints. The test is done during the coding process rather than postponing the test. In TDD, each feature begins with writing a test case that defines the expected behaviour. After making the test case, the developer writes the required code to pass the test. 

In Agile development, coding and test automation are developed at the same time. As soon as a requirement is identified in Jira, developers can begin building the feature while test cases and the automation scripts for the tests are created concurrently.

This means that unit tests will validate very small pieces of code, integration tests will verify the combination of components, and end-to-end tests will confirm the complete product’s behavior meets expectations without waiting until the end of the sprint.

Development and Test Automation Sprints for TDD

The shift-left approach reduces feedback loops, leaving the defects when they are made. The net effect is low, rapid recurrences, and a better quality of code inserted into production at the end of the sprint has been improved.

To discover how Test-Driven Development can change your product development cycle with improved code quality, faster delivery, and lower maintenance costs. Let’s connect and discuss how MosChip can help implement TDD practices that drive continuous quality in your software solutions.