What is Behavior-Driven Development (BDD)?
Published: 2024-02-01 15:56:16

If you're a good developer looking at how you can write clean, maintainable software and researching different software development processes, you've probably seen acronyms like BDD, TDD, ATDD, DDD,... and you realize there are so many 'didies,' and you just can't stop looking at them, which is a good thing. It means that you're hitting your puberty as a software engineer and entering your over-engineering era. Learning all of these may be necessary, but can also be confusing. So, let's explore them one by one. Today, we're checking out the 'B' one, or Behavior-Driven Development.

Since Wikipedia is such a great source of knowledge (jk), let's see what it has to say about Behavior-Driven Development.

> _Behavior-Driven Development (BDD) is a software development process that encourages collaboration among developers, quality assurance experts, and customer representatives in a software project. It encourages teams to use conversation and concrete examples to formalize a shared understanding of how the application should behave. It emerged from Test-Driven Development (TDD) and can work alongside an agile software development process. Behavior-Driven Development combines the general techniques and principles of TDD with ideas from Domain-Driven Design and object-oriented analysis and design to provide software development and management teams with shared tools and a shared process to collaborate on software development._

This is what Wikipedia says about BDD, and I'm too dumb to understand it, so let's break it down.

I think the best way to understand something is to understand the problem it actually solves. So, let's consider a problem scenario where BDD would be a good fit.

### **Scenario**

So, I spent weeks researching hundreds of companies of different sizes that were trying to automate their processes by developing software. I created a dataset of these companies to pinpoint exactly which size, which domain, and how much technical expertise is needed for BDD to be a good fit.

Just kidding, I asked ChatGPT to come up with a scenario, and it came up with this.

> _A boutique hotel wants to develop an online booking system. The hotel management has specific ideas about how the system should work, but they are not technically savvy. They've experienced issues in the past where delivered software did not match their expectations, leading to significant rework and dissatisfaction. The development team, on the other hand, is technically proficient but lacks a deep understanding of the hotel's unique booking requirements and guest management processes._

I actually think this is a great example. Notice how it mentions their previous bad experience with the developed software, as if you must have experienced developing bad software to truly appreciate the beauty of BDD, which I think is true. Almost all of us have experience with software that, in some way, does not meet the stakeholders needs. A software project, if not managed properly, can easily be derailed in a way which is not expected by the stakeholder (with a lot of fancy useless features just to bloat the software and no answers to the stakeholders original needs). Even good software usually turns out to be a lot different from the original vision.

Even with adopting agile methodologies and defining user stories, having a QA team, having sprints, and coming up with an MVP at the start, and standing up when we talk to each other, the problem can still remain. So, how can we avoid these problems? How can we minimize wasted development time as much as possible?

*Enter BDD.*

No, actually wait, let's have a brief look at DDD and TDD first.


### **Test-Driven Development (TDD)**

Test-Driven Development (TDD) is a software development process relying on software requirements being converted to test cases before software is fully developed, and tracking all software development by repeatedly testing the software against all test cases. This is as opposed to software being developed first and test cases created later.

Ok, but why use it?

1. **Improved Code Quality**: Writing tests first requires thinking through the requirements and design before writing the code, which can lead to better-designed, more reliable, and maintainable code. It also helps in catching defects early in the development cycle, reducing the cost of bug fixes.
    
2. **Clearer Specifications**: TDD encourages developers to consider the desired outcome and how to test it before writing the code. This leads to a clearer understanding of the feature's requirements and how it should behave, thus reducing ambiguities.
    
3. **Simpler Design and Implementation**: By focusing on small, incremental steps (write a test, make it pass, refactor), TDD can lead to simpler and more modular code. Developers are less likely to add unnecessary features, keeping the codebase lean and focused on what is needed.
    
4. **Facilitates Refactoring**: With a comprehensive test suite, developers can refactor code with confidence, knowing that tests will catch any regressions or unintended side effects. This encourages continuous improvement of the code.
    
5. **Documentation**: The test cases themselves serve as documentation for the system. They clearly demonstrate what the code is supposed to do, which is helpful for new developers joining the project or when revisiting an older codebase.
    


### **Domain-Driven Design (DDD)**

Domain-Driven Design (DDD) is a software development approach that focuses on modeling software based on the real-world business domain it aims to serve. The core idea is to align the software architecture and development practices with the business domain's complexities. This approach emphasizes collaboration between technical and domain experts to gain a deep understanding of the domain, which in turn informs how the software is structured. Key concepts in DDD include the ubiquitous language, a shared language between developers and domain experts, entities and value objects that model domain concepts, and bounded contexts that define logical boundaries in the domain. By doing so, DDD helps create software systems that are more meaningful, flexible, and aligned with business needs, enabling them to evolve as the domain itself evolves.


### **So, what does it have to do with BDD?**

Behavior-Driven Development (BDD) takes the foundational principles of TDD – writing tests first and focusing on small, incremental development steps – and combines them with the domain-centric approach of DDD. It emphasizes collaboration, a shared language, and a focus on defining and delivering business value, making it a powerful methodology for developing software that meets both technical and business requirements effectively.

**The TDD Part:** While TDD focuses on the developer's perspective and involves writing tests before code, BDD extends this concept to the business and user perspective. BDD encourages writing behavior specifications rather than traditional test cases. These specifications are written in a language understandable by all stakeholders, including non-technical members, ensuring that everyone has a clear and shared understanding of the expected behaviors of the software.

**The DDD Part:** BDD benefits from the principles of DDD, with the focus on a ubiquitous language and a deep understanding of the domain. By using a language consistent across both the development team and the business stakeholders, BDD ensures that the software developed is closely aligned with the business requirements and domain realities. The emphasis on behavior rather than just technical implementation helps in bridging the gap between technical and non-technical stakeholders.

**Specification by Example:** A key practice in BDD is specifying behavior through examples, which are essentially concrete scenarios (kind of like user stories) illustrating how the software should behave in various situations. These examples serve as a basis for developing tests and guide the development process. This approach ensures that the software functionality is directly linked to the business requirements.

**Collaboration and Communication:** BDD places a strong emphasis on collaboration between developers, QA professionals, and business stakeholders. By involving all parties in the discussion and formulation of behavior specifications, it ensures a shared understanding and minimizes the risk of misinterpretation of requirements.

**Continuous Feedback and Iterative Development:** Similar to TDD, BDD promotes an iterative development process where features are continuously tested, and feedback is rapidly incorporated. This approach helps in identifying issues early in the development process, reducing the time and cost of addressing them later.

**Tools and Automation:** BDD uses tools that allow specifications to be written in a natural language-like format, which can then be tied to the automated tests. This makes the specifications both readable and executable, ensuring that they are always up-to-date with the current state of the system.

**Focus on Customer Value:** Both DDD and BDD emphasize delivering value to the business or end-user. By ensuring that the software developed is directly aligned with the business needs and by providing a clear way to describe and verify this alignment, BDD ensures that the final product delivers real value to its users.

So, there you have it, a casual stroll through Behavior-Driven Development (BDD). It's more than just a process; it's like having a GPS for your project, making sure you're always on the right path. BDD is kind of like glue attaching everyone, from coders to clients, together and bringing them on the same page.

Stay tuned, as in the next article we'll dive into actually putting BDD into action in your projects. We'll be looking at how to make this more than just fancy tech talk and turn it into real, usable strategies that fit right into what you're working on.