As the demand for advanced medical devices continues to grow, so does the need for clean, effective software to power them. Creating such a thing, of course, is much easier said than done. Especially in the MedTech market where devices are required to complete complex tasks and any error in coding has the potential to cause harm or even death to the user.
Testing plays a critical role in ensuring the safety and efficacy of medical device software. But not all testing methodologies are created equal.
In this article, we look at the importance of test-driven development in the creation of medical device software. We’ll compare this agile approach to coding with less rigorous, less effective waterfall-style approaches and look at the benefits the former has for developers, stakeholders, and end users. Lastly, we’ll discuss the importance of partnering with a software development team that understands and utilizes TDD in the pursuit of bringing your medical device idea to market.
Understanding Test-Driven Development
Unless you’ve spent considerable time working as a software developer in an agile workflow, you likely don’t have a strong understanding of what test-driven development (TDD) means or what the process looks like. To understand why this methodology is so vital to building safe and effective MedTech, you first need to understand these key principles.
What Is TDD?
Test-driven development is an approach that places a strong emphasis on writing tests before writing the actual code.
The primary goal of TDD is to ensure the reliability, maintainability, and correctness of the software through a continuous cycle of writing tests, writing code to pass those tests, and then refactoring the code to improve its structure while keeping all tests passing. In the context of building medical device software, TDD becomes especially crucial due to the high stakes involved in ensuring the safety and effectiveness of the medical devices.
Test-driven development follows a continuous five-step workflow based on the key principles of this approach.
- Write Tests First. Tests are written before any production code, allowing developers to establish a clear understanding of the desired behavior and functionality of the software before it is created. This helps in aligning the software development process with the intended specifications and requirements, ensuring that critical functionalities are properly addressed and tested.
- Write the Minimum Code to Pass the Test. Developers only write as much code as necessary to make the currently failing test pass. This principle encourages a focus on meeting the specific requirements outlined in the tests without unnecessary complexity.
- Run Tests Frequently. The failed test should be rerun and passed to confirm the new software works as intended. All tests should be rerun frequently to ensure additional code changes do not cause defects.
- Refactor Code. Once a code has successfully passed the test, it is refactored to improve its structure and maintainability while keeping all tests passing.
- Automate Testing. Tests are automated and run as part of the continuous integration process.
How Does TDD Differ from Traditional Testing Methodologies?
TDD diverges from traditional testing methodologies in its fundamental approach to software development.
In TDD, developers begin by crafting tests that define the expected behavior before writing any code. This proactive strategy aims to prevent defects by catching and addressing issues early in the development cycle.
Traditional testing often follows a more reactive model, with testing occurring after the code has been implemented. The focus is on detecting and correcting defects in a separate phase, often leading to longer feedback loops and delayed issue identification. The number of bugs revealed in this final phase of testing is often very high, requiring extra weeks to months to fix. Using this methodology can lead to higher project costs and longer development times.
Iterative and Incremental Nature of TDD
The process of TDD unfolds iteratively, with developers repeatedly cycling through short phases of test creation, code implementation, and refactoring.
This iterative cycle is well-suited for the complex and evolving nature of medical device software. Medical devices often undergo numerous revisions, incorporating feedback from regulatory bodies, healthcare professionals, and end-users. The iterative nature of TDD allows developers to adapt swiftly to changing requirements, ensuring that each iteration builds upon the successes and lessons learned from the previous ones.
TDD also advocates for incremental development, where the software functionality is built and enhanced gradually over time. This aligns seamlessly with the phased and regulated nature of MedTech development.
Incremental development in TDD ensures that each new piece of functionality is thoroughly tested before being integrated into the existing codebase. For medical devices, this approach is crucial as it allows for systematic validation and verification at each stage, reducing the likelihood of critical errors that could compromise patient safety or regulatory compliance.
Benefits of TDD in Medical Device Software Development
Just from the short discussion on test-driven development above, you can already see that TDD has many benefits for medical software device development over traditional testing approaches.
The full scope of TDD’s benefits for building software as a medical device (SaMD) include:
- Early Detection of Defects. This proactive approach helps catch issues at the inception of development, reducing the likelihood of critical errors in medical device software. The continuous testing throughout development ensures that each new piece of functionality is thoroughly validated, reducing the risk of introducing errors and enhancing the overall quality of the SaMD.
- Regulatory Compliance. By having a set of tests that define and validate the expected behavior of the software, TDD aids in demonstrating compliance with stringent regulatory standards, such as those set by the FDA or ISO. Additionally, test cases serve as explicit and executable specifications of the software’s intended behavior, aiding in maintaining traceability between requirements, design, and implementation.
- Reduced Debugging Time. Since failing tests are identified immediately, developers can pinpoint the source of problems more efficiently, leading to quicker resolutions and a streamlined development process.
- Facilitates Code Refactoring. The confidence provided by a comprehensive suite of tests allows developers to make improvements to the codebase without fear of introducing defects, resulting in a more maintainable and adaptable software architecture.
- Enhanced alignment between developers and stakeholders. Clear, executable tests serve as a common language that can be understood by both technical and non-technical team members, facilitating communication and ensuring a shared understanding of the software’s functionality.
- Faster Time-to-Market. The early detection of defects, reduced debugging time, and improved code quality contribute to a more efficient development process, potentially accelerating the time-to-market for medical devices.
- Enhanced Adaptability. Refactoring ensures that the code remains clean, efficient, and compliant with regulatory requirements, technological advancements, and market changes. This principle is critical for the long-term maintainability and adaptability of medical device software.
TDD vs Behavior-Driven Development
Closely related to test-driven development is behavior-driven development (BDD). This method is an evolution of TDD that provides many of the same benefits when developing software for medical devices and SaMD. But there are some notable differences between these approaches that those in the MedTech industry should be aware of.
BDD extends the principles of TDD by emphasizing the behavior of a system rather than just its individual units.
Tests in TDD involve validating the behavior of individual units or components of the software. These tests are often more fine-grained, focusing on specific functionalities or methods. BDD, on the other hand, involves writing tests that validate the behavior of the entire system or features from an end-user perspective. Scenarios are written in a more coarse-grained manner, addressing higher-level functionalities.
Another key difference is the language used to create these tests.
BDD focuses on enhancing collaboration and communication between different stakeholders, including developers, quality assurance professionals, investors, and other non-technical parties. In order to foster this broad collaboration, tests are written in natural language that all team members, technical and not, can understand. These statements are often referred to as “Given-When-Then” statements and describe the expected behavior of the software in a human-readable format.
This differs from TDD tests, which generally focus on technical aspects. These tests are written by developers in the language of the programming framework. They center around the code and its internal design.
While these two methodologies do have some key differences, there is heavy overlap between them. This article focuses on the use of TDD, as it is the more popular methodology in the industry, and because most of its benefits also apply to BDD. But do note that there are some additional benefits of BDD that may make it a better option for developing your SaMD.
Importance of Quality Assurance in Medical Device Software
Quality assurance (QA) in medical device software plays a critical role in ensuring the safety, efficacy, and compliance of these complex systems. QA and TDD are interconnected methodologies that complement each other in the development of SaMD. Their integration enhances the overall quality, reliability, and safety of the software.
The development of medical device software is governed by stringent regulatory frameworks set by health authorities such as the FDA and international standards like ISO 13485. Compliance with these regulations is imperative to ensure the safety, efficacy, and quality of medical devices. Regulatory bodies establish guidelines that cover the entire software development lifecycle, emphasizing the importance of documentation, risk management, and validation. Quality assurance practices, therefore, must align closely with these requirements to obtain regulatory approvals and maintain the integrity of medical device software.
These regulations are vital as software failures in medical devices can have severe consequences, ranging from patient safety risks to legal and financial implications for manufacturers. Malfunctions or errors in medical device software can compromise the accuracy of diagnostics, treatment delivery, or patient monitoring. In critical situations, software glitches may lead to incorrect readings, delays in treatment, or even catastrophic outcomes. The potential for harm underscores the critical need for robust quality assurance measures to minimize the risk of software failures in medical devices.
Ensuring the quality and reliability of medical device software requires a proactive and robust QA process. In this context, QA involves systematic and comprehensive testing, validation, and verification activities throughout the software development lifecycle. A proactive approach means addressing potential issues early in the process, starting from the requirements phase through design, implementation, and testing. In many ways, TDD functions as a proactive QA approach in SaMD and medical device development.
TDD as a Proactive Quality Assurance Approach
By shifting the focus from reactive testing to the early prevention of defects, test-driven development functions as a proactive QA approach when building SaMD. Specifically, it helps to detect defects early, create integrated, automated tests, mitigate risks, and conform to regulatory compliance.
Early Defect Detection
By requiring developers to write tests before implementing the actual code, TDD helps ensure early defect detection. If the newly implemented code fails to pass these tests, it immediately signals a defect or deviation from the intended functionality. This early and continuous validation process ensures that defects are identified at the smallest scope possible, enabling developers to address issues promptly before they can escalate into more complex problems.
Continuous Integration and Automated Testing
The development cycle of TDD aligns seamlessly with continuous integration practices, as developers integrate their changes frequently into the main code repository. Automated testing plays a central role in TDD, too, with tests executed automatically each time new code is added. This ensures that the existing codebase remains stable and that new changes do not introduce regressions.
Mitigates Risks
Through the creation of tests before code implementation, TDD helps developers thoroughly validate critical functionalities and scenarios. This proactive stance minimizes the risk of defects that could compromise the safety and reliability of medical software. TDD’s continuous validation, risk coverage in test scenarios, and the ability to catch issues at their inception contribute to a more resilient development process. This reduces the likelihood of errors that could have adverse consequences in the context of medical applications.
Regulatory Compliance
TDD’s test-first approach ensures a clear and documented specification of the software’s expected behavior, serving as a form of living documentation. This aligns seamlessly with the documentation requirements outlined by regulatory frameworks, aiding in audits and submissions. The systematic and proactive nature of TDD contributes to the reliability and predictability of the software. These factors are critical for meeting regulatory standards and obtaining approvals in the highly regulated field of medical devices.
Choosing the Right Software Development Partner
When choosing a software development partner to help bring your medical device or SaMD to life, it is critical to consider their software testing methodology.
Many software companies, especially those who do not specialize in the MedTech world, rely on waterfall and linear methodologies both with respect to software development and testing. While these approaches can work for creating more traditional tech, they are far too rigid and not efficient enough to create safe and effective SaMD.
Because this approach to development often leads to a final product riddled with bugs that need to be corrected, it can be more costly and time-consuming to build medical software this way. The road to market can be even further drawn out due to a lack of reliable documentation necessary to meet regulatory compliance requirements.
Many software companies working in the medical technology field claim to utilize TDD or BDD methodologies when, in fact, their processes involve a minimal number of unit tests. These companies often complete most of their testing manually in a waterfall manner.
This is why it’s vital to choose a software partner that has extensive experience with TDD and BDD and one that openly states their minimum code coverage in the contract.
Here at Sequenex, we are fully invested in a test-first approach and test-driven methodology. We use TDD when creating software for our clients because it reduces defects, improves reliability, ensures documentation and regulatory compliance, and produces a safer product that is highly adaptable to changing regulations and an ever-advancing market.
If you have questions about how utilizing test-driven development can help your company save money and produce a better device, we would love to speak with you. Our decades of experience and a development team dedicated to TDD principles mean we have the knowledge to answer your questions and bring your medical device to market faster and for less. Connect with us today!