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  • Writer's pictureCraig Risi

The Importance of Testability on Software Architecture

The design of software architecture serves as the foundation upon which the entire software system is built. A well-designed architecture is crucial for the overall operation of the software and determines how well software can scale its reliability, performance, and maintainability.

However, while many architects will design software built around its functional usage and keep the performance and security of the software in mind, testability is often an important factor of software architecture that doesn’t get enough focus. Software that is easier to test, tends to not only make the approach to testing – and important – automation far simpler, but will often even lead to a better-quality design.

Additionally, if we consider the average software development process over several sprints – we typically see teams spending far more time with the testing effort than they do on the developing effort alone. And this is even with the most agile of teams. The reason for this is that the software is often simply not designed with the idea of test automation in mind, meaning that the only way teams can properly ensure the software is working correctly is by relying on extensive manual testing which significantly slows down the development timelines. Or attentively, where the testing is automated, its often reliant on clunky end-to-end automation which tends to fail often and therefore leads to additional maintenance effort and unreliable results.

With the speed of delivery and rapid deployment such important traits in software architecture, it’s critical that we ensure that software can then be appropriately designed around these constraints, ensure that testing can be easily reliably automated throughout the cycle and therefore consistently deployed and maintained throughout.

Benefits of Testability to Software Architecture

However, outside of just these areas, the benefits of considering software architecture based on its testability are numerous with below providing some of the most important facets to be aware of:

Early Detection of Defects: A testable architecture allows for the early detection of defects in the software development lifecycle. By designing software with testability in mind, developers can create automated tests that check for correctness and identify issues before they propagate through the system.

Facilitates Change and Maintenance: Testable software architectures are typically more modular and loosely coupled. This makes it easier to make changes to the codebase without inadvertently breaking other parts of the system. When components are isolated and can be tested independently, developers can refactor or add features with greater confidence.

Reduces Regression Issues: Regression testing ensures that changes made to the codebase do not inadvertently introduce new bugs or regressions into the system. A testable architecture enables comprehensive regression testing, allowing developers to verify that existing functionality remains intact after modifications.

Supports Continuous Integration and Deployment (CI/CD): Testable architectures are well-suited for continuous integration and deployment practices. Automated tests can be integrated into the CI/CD pipeline to ensure that each code change passes a battery of tests before being deployed to production. This helps maintain a high level of software quality and reliability.

Improves Collaboration: Testable architectures promote collaboration among team members. Clear and understandable tests serve as living documentation that helps developers understand the behaviour of the system. Additionally, when tests are automated, team members can easily validate each other's changes and ensure that they meet the desired specifications.

Enhances System Reliability and Maintainability: By identifying and fixing defects early in the development process, testable architectures contribute to the overall reliability and maintainability of the software system. This leads to a more stable and robust product that is easier to maintain over time.

Reduced Time-to-Market: Automation in testing speeds up the feedback loop in the development process. By automating tests, architects can ensure rapid validation of changes, leading to faster delivery of features and updates to end-users.

Cost Savings: Investing in automation and testability upfront can result in significant cost savings over the long term. Automated tests reduce the need for manual testing efforts, saving time and resources. Additionally, catching defects early in the development process avoids costly rework and maintenance later on.

Enhanced Agility: Testable architectures support agile development practices by enabling frequent releases and iterations. Automation allows teams to quickly validate changes and respond to evolving requirements, fostering greater adaptability and agility in the software development process.

Customer Satisfaction: Ultimately, focusing on automation and testability leads to better software products that meet or exceed customer expectations. By delivering high-quality software with fewer defects and faster turnaround times, architects contribute to improved customer satisfaction and loyalty. 

How do we make software architecture more testable?

So, at this point in time, it should be easy to see the benefits of considering testability in the overall architectural design and the impact it has on the software we are developing. This leads to the question though of how we go about ensuring that our software is designed in a more testable manner.

The reality is that this is not something that can be easily done and there are many things worth considering. Especially when needing to balance the overall purpose of the software with the require performance and security criteria while still ensuring its testability. However, the following factors contribute to making software more testable: and should be the main consideration for any architect in working with software appropriately.

Modularity: Breaking down the software into smaller, modular components makes it easier to isolate and test individual units of functionality. Each module should have well-defined boundaries and clear interfaces, allowing for independent testing.

Encapsulation: Encapsulating data and behavior within modules or classes prevents direct access from external components, promoting better control over the testing environment. This reduces dependencies and facilitates unit testing by focusing on the unit's internal state and behavior.

Loose Coupling: Minimizing dependencies between components reduces the likelihood of ripple effects when making changes to the codebase. Loose coupling enables easier substitution of dependencies with mock objects or stubs during testing, facilitating isolation and independence of tests.

High Cohesion: Components with high cohesion have a clear, single responsibility, making them easier to understand and test. Well-structured code with cohesive components leads to more focused and targeted tests, improving test coverage and effectiveness.

Clear Interfaces: Defining clear and consistent interfaces between components promotes interoperability and testability. Interfaces serve as contracts between components, allowing for easier integration testing and interchangeability of implementations, such as using mock objects for testing.

Dependency Injection: Dependency injection separates the creation and management of dependencies from the dependent components, making it easier to replace dependencies with mock or stub implementations during testing. This promotes flexibility and testability by decoupling components and facilitating dependency inversion.

Testable Architecture Patterns: Architectural patterns such as MVC (Model-View-Controller), MVP (Model-View-Presenter), MVVM (Model-View-ViewModel), and Clean Architecture emphasize separation of concerns and promote testability by defining clear boundaries between presentation logic, business logic, and data access layers.

Automated Testing Support: Building support for automated testing into the development process, including unit tests, integration tests, and end-to-end tests, facilitates continuous validation of the software's behavior and functionality. Automated tests should be easy to write, execute, and maintain, encouraging developers to incorporate testing into their daily workflow.

Mocking and Stubbing: Using mock objects or stubs to simulate dependencies during testing helps isolate the unit under test and control its behavior. Mocking frameworks provide tools for creating and configuring mock objects, making it easier to emulate external dependencies and interactions.

Test Data Management: Providing mechanisms for managing test data, such as fixtures, factories, or test data generation tools, simplifies the setup and teardown of test environments. Test data management ensures consistency and repeatability of tests, reducing the likelihood of false positives or negatives.

Testability in different architecture types

Each architecture type has its own set of advantages and challenges when it comes to testing. The suitability of a particular architecture for testing depends on factors such as the nature of the application, the development team's expertise, and the available testing tools and infrastructure.

So below we will look at many of the different popular architecture design and brief provide the benefits and cons that they offer from a testing perspective. While the final architectural design pattern decided on needs to consider a variety of factors – having a good understanding of these testing concerns should held lead the architect to make the right decisions that determine the overall software design. 

Now, there is a lot more to architectural design and there are many different patterns to consider, but for this article, we will focus on the most common architectural styles and patterns.

Monolithic Architecture:


  • Simple to test: With all components tightly integrated, testing can be straightforward.

  • Easier to set up end-to-end tests, though if done poorly, they tend to break frequently.


  • Lack of modularity can make it difficult to isolate and test individual components.

  • Long feedback loops: Changes to one part of the application may require extensive regression testing.

Microservices Architecture:


  • Individual services can be independently tested, allowing for easier isolation and targeted testing.

  • Facilitates parallel development and testing of different components.


  • Requires additional effort to set up and maintain a testing infrastructure for distributed systems.

  • Integration testing between services can be complex and resource-intensive.

Service-Oriented Architecture (SOA):


  • Encourages reusability and interoperability of services, which can lead to more modular and testable components.

  • Services can be tested independently before integration.


  • Similar to microservices, integration testing can be challenging due to dependencies between services.

  • Overhead in managing and coordinating service interactions.

Event-Driven Architecture:


  • Supports asynchronous communication between components, enabling more decoupled and testable systems.

  • Events can be replayed for testing purposes, facilitating scenario-based testing.


  • Testing event-driven systems requires specialized testing techniques and tools.

  • Ensuring message ordering and delivery guarantees can be challenging.

Layered Architecture:


  • Clear separation of concerns between layers facilitates testing at each level (e.g., unit testing, integration testing).

  • Encourages the use of interfaces, which can aid in creating mock objects for testing.


  • Tight coupling between layers may hinder independent testing of components.

  • Changes in one layer may necessitate changes in other layers, leading to cascading test updates.

Component-Based Architecture:


  • Promotes reusability and encapsulation of components, making them easier to test in isolation.

  • Components can be tested independently before integration into the larger system.


  • Testing interactions between components can be complex, especially if dependencies are not well-managed.

  • Component interfaces and contracts must be well-defined to ensure accurate testing. 


Considering testability in the design of your software has a massive impact on the system being designed and if you aren’t already considering this as an architect -  then you need to start looking at how your software design is impacting your testability.

Many companies have lost faith in the software testing process because of how much it slows down their ability to deliver and the difficulty of building reliable automation systems to ensure this quality. The reality though is that it’s not about the process of testing itself, but rather the design of the software in supporting the testing effort that makes a big difference. So hopefully, as companies look to deploy features more frequently through automated CI/CD processes, they will consider the best architectural approaches that will help make this a reality for them.



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