Lean Software Development: Building with Quality

Part one of a series on how to build with quality based on Lean Software Development principles. In this article, we explore what “quality” really means, how it differs from the traditional approach, and what principles help us prevent errors from becoming defects.

Lean Software Development: Building with Quality

One of the main differences between Lean Software Development and traditional approaches lies in the treatment of quality—both in the resulting software or product and in the work environment (collaboration, tools, communication).

Lean Software Development considers quality as an integral part of the product’s value, essential to deliver value to the customer as efficiently as possible. From this perspective, all quality issues are considered one of the main wastes to eliminate.

In contrast, traditional approaches usually focus primarily on the quality of the final product. Lean, on the other hand, focuses on the continuous improvement of the processes and the system that generates the final product.

Quality control, which traditionally focuses on inspecting the product at the end of the process, becomes in Lean a fundamental part of each stage. In other words, instead of inspecting and validating quality at the end, quality is built in from the beginning and maintained throughout the process. This involves moving from a reactive approach to problems to a more proactive one, making any issues visible with the goal of solving them immediately and addressing root causes (system or processes).

We can summarize these differences as follows:

Focus

• Traditional: Mainly on the quality of the final product.
• Lean Software Development: Continuous improvement of processes and systems.

Quality Control

• Traditional: Inspection at the end or at specific production checkpoints.
• Lean Software Development: Built-in quality at every step (jidoka).

Problem Solving

• Traditional: Reactive, addressing problems after they occur.
• Lean Software Development: Proactive, highlighting and solving problems immediately.

In the end, Lean Software Development considers that all rework (incidents, bug fixing, repeated processes, etc.) caused by problems and defects is one of the major wastes to eliminate. Therefore, it focuses on introducing quality at every step of the process, minimizing waste, and fostering a habit of working with quality and continuously improving.

Quality is a broad concept that can cover various aspects: external quality (how it is perceived by the customer or end user), internal quality (related to the ease of evolution and maintainability of the code or system), and even the quality of our processes and work environment.

In this article series, we will place special emphasis on external quality, as perceived by customers or users. However, we will also address aspects of internal and process quality, since they are fundamental for sustaining high external quality in the long term. In addition, since Lean Software Development places strong emphasis on continuous improvement of both the processes and the system to ensure such quality, we will also address aspects related to process and work environment quality.

Basic Concepts

Let’s start with some concepts and definitions that will be useful throughout the rest of the articles:

• Error: We consider an error as any deviation from the expected result. For example, in our application’s execution, an error may be a failed test, code that functionally does not meet expectations, among others.
• Problem: In the context of Lean Software Development, a problem is any obstacle that prevents us from delivering value to the customer in the most efficient and effective way. This includes the gap between the current state and the desired state, but also covers situations such as: Ambiguous requirements leading to incorrect implementation. Communication problems within the team that result in misunderstandings and delays. Technical limitations preventing desired performance.Inefficiencies in the deployment process causing delays.
• Defect: A defect is an error that prevents the product from fulfilling its function or purpose, directly affecting customers. Defects are one of the main sources of waste identified in Lean Software Development (see “Eliminating Waste in Development”). Therefore, it is a priority to avoid them whenever possible and eliminate them immediately when detected. The linked article explores how Lean Software Development adapts the seven types of waste from Lean Manufacturing to software, focusing on eliminating activities that do not add value to the customer and promoting practices like reducing “Partially Done Work” and avoiding “Extra Features and Code.” See article for more details.

It is important to remember that defects are a subset of errors, and problems can include multiple errors and defects.

Although this classification may seem confusing at first, distinguishing between problem (a general situation that includes errors and defects), error (any deviation from expectations, like a failed test, an incorrect variable name, or a poorly implemented feature), and defect (an error that affects the customer or the system’s purpose and is a fundamental source of waste) helps us better understand the situation and define appropriate processes to address each case.

Lean Approach to Reducing Errors and Defects

• Jidoka: Also known as "autonomation", this principle seeks to detect and correct defects automatically, stopping production as soon as an error is identified. A classic example in Lean Manufacturing is the use of “Andon Cards,” visual signaling systems that allow any worker to stop the production line upon detecting a problem. In our software development context, this translates to automated testing at different stages, alarms and monitoring, the use of a CI pipeline that stops deployment if tests fail, among other mechanisms.
• Poka-Yoke: Translated as "mistake-proofing", this approach relies on systems and designs that prevent human errors. In software development, Poka-Yoke applies both to our internal processes and the user's interaction with the product. In the development process, we implement Poka-Yoke through practices such as using strongly typed programming languages, tools with optimal default settings, automated tests, ValueObjects, and preconditions. These techniques help prevent coding and design errors. In software usability, we apply Poka-Yoke through error-prevention systems, effective contextual help messages, and intuitive designs. This is where User Experience (UX) plays a crucial role. Although UX is not a direct Poka-Yoke mechanism in the technical sense (like a physical sensor stopping a machine), it shares the fundamental goal of preventing user errors. Good UX design anticipates possible mistakes, guides the user clearly, and provides immediate feedback, significantly reducing the chances of user error. In this sense, UX complements and reinforces Poka-Yoke principles, ensuring the software is as intuitive and error-free as possible for the end user.
• Kaizen: This is the principle of continuous improvement applied to our processes and systems. As one of the pillars of Lean, it promotes the constant search for ways to reduce errors and improve quality, both in the product and in the processes and tools we use.

Avoiding Errors from Becoming Defects

In all the teams I’ve worked with, we make mistakes continuously. Some are just development process errors, while others are misunderstandings. The latter arise because we’re constantly learning about the problem. This is the reality: we make mistakes constantly, and everyone I know in this profession makes them. Some more, some less, but no one is error-free.

If we acknowledge and accept this reality, the important thing is to understand that the goal is not to completely avoid errors (something impossible), but to ensure that those errors don’t become defects that impact the final user experience. The article “Be humble, no rockstars allowed” advocates for humility and teamwork in software development, emphasizing that continuous learning and effective error management are crucial—rather than relying on individual “rockstars.” See article for more.

This is Lean Software Development’s approach: acknowledge and accept that we make mistakes, and focus on having a process that allows us to detect them, protect ourselves from them continuously, resolve them, and prevent them from becoming defects.

How do we achieve this?

1. Incorporating quality in every phase of development, automated whenever possible (Jidoka + Poka-Yoke).
2. Continuously improving the mechanisms and techniques that ensure quality at each stage (Kaizen).

In the next article, we will explore how to detect errors as early as possible, stop the flow when they appear, and learn from them without pointing fingers. This could mean stopping the CI/CD pipeline if an integration test fails, blocking code commits if unit tests don’t pass, stopping a pairing session if a critical error is discovered, or even temporarily halting new feature development to address a severe performance issue. Because working with quality also means having a strategy so that errors don’t become defects.