Agile criteria for good requirements – INVEST

In Agile development, the quality of user stories is paramount to the success of a project. Requirements size also plays a key role: to consider requirements ready for development they should be small enough to be implemented by the team within a single iteration. The INVEST criteria provide a comprehensive framework to ensure that user stories are well-formed, bite-sized and effective.

INVEST stands for Independent, Negotiable, Valuable, Estimable, Small, and Testable. This post will delve into each of these criteria, explaining their importance and how they contribute to the creation of high-quality user stories.

Independent. User stories should be self-contained and not dependent on other stories for completion. This independence allows for greater flexibility in planning and execution, as stories can be developed and tested in isolation without causing bottlenecks or delays in the project timeline. For example, a user story like “As a customer, I want to search for products by category so that I can find the products I am looking for more easily” can be developed independently of other features.

However, in complex projects achieving independent requirements is hardly possible. If, for example, we have broken a process down into its steps, then those steps are clearly dependent on one another in sequentially carrying out that process. If we have broken the process down into variants by product type or customer segment, on the other hand, dependencies will exist between requirements that have common process steps, a data model, or an interface.

Our goal here is not in fact to create independent requirements, but rather to create requirements for which the dependencies are made as clear as possible. And the best way of doing this is to make those dependencies explicit in the structure of requirements hierarchy, rather than hidden within the requirement itself. This is what will best support the prioritisation and management of those requirements.

Negotiable. User stories should not be rigid specifications but rather prompts for discussion and refinement between the development team and stakeholders. This negotiability ensures that the requirements can evolve based on feedback and changing needs, fostering better collaboration and alignment with stakeholder expectations. This approach helps avoid the pitfalls of overly detailed and inflexible requirements that can become obsolete or misaligned with user needs.

Valuable. Every user story must clearly capture the value it will deliver to the end user or customer. This focus on value ensures that the development efforts are aligned with the overall goals of the project and that each story contributes meaningfully to the product. For instance, a story that allows users to filter search results by category directly enhances the user experience by making it easier to find desired products.

Estimable. For a user story to be effective, it must be defined clearly enough that the development team can estimate the effort required to complete it. It is crucial for planning and resource allocation, helping teams to manage their workload and set realistic timelines. Clear and concise stories enable better estimation and reduce the risk of underestimating the complexity of a task.

Small. User stories should be small and focused, capturing the smallest possible increment of customer value. Smaller stories are easier to manage, develop, and test within a single iteration, reducing the risk of delays and ensuring continuous delivery of value. Breaking down larger tasks into smaller, manageable stories helps maintain momentum and allows for more frequent feedback and adjustments.

Testable. A good user story must be testable, meaning that there are clear, objective criteria for determining whether the story was successfully implemented as intended. Testability ensures that the development team can verify the completion of a story and that it meets the defined requirements. Clear acceptance criteria are essential for validating the functionality and ensuring that the story delivers the intended value.

And stories have to include sufficient details about test cases or acceptance criteria. This represents an agreement on the things that the developers have to demonstrate to the Product Owner at the end of an iteration.

Conclusion

The INVEST criteria provide a robust framework for evaluating and improving the quality of user stories in Agile development. By ensuring that stories are Independent, Negotiable, Valuable, Estimable, Small, and Testable, teams can enhance collaboration, transparency, and alignment with stakeholder needs, ultimately leading to more successful project outcomes. Consistently applying these principles helps create a solid foundation for Agile projects, enabling teams to deliver high-quality software that meets user needs and expectations.

However, it’s not the only tool you have at your disposal. If a requirement is still too large to fit into one iteration you have several tactics to split them still trying to preserve independence and value as much as possible.

Further Reading

• Online article “Splitting Requirements at Scale. Strategies for building manageable requirements hierarchies in complex problem domains” by Gareth Rogers published at RE Magazine;
• A free IREB RE@Agile handbook focused on tools and techniques of Requirements Engineering in Agile.