Test-driven development (TDD) is a common agile programming technique which has both specification and validation aspects. With TDD, you specify your software in detail on a just-in-time (JIT) basis via executable tests that are run in a regression manner to confirm that the system works to your current understanding of what your stakeholders require.
TDD is the combination of test-first development (TFD) and refactoring. With TFD, you write a single test (at either the requirements level with customer/acceptance tests or the design level with developer tests) and then you write just enough software to fulfill that test. Refactoring is a technique where you make a small change to your existing code to improve its design without changing its semantics.
TDD offers several benefits:1. It enables you to take small, safe steps during development, increasing programmer productivity.2. It increases quality. Agile developers are doing more testing, and doing it more often, than ever before. We're also fixing the problems that we find right on the spot.3. It helps to push validation activities early in the lifecycle, decreasing the average cost to fix defects (which rises exponentially the longer it takes you to detect them).4. Through single sourcing information, by treating tests as both specifications and as tests, we reduce the work required, increasing productivity.5. We leave behind valuable, up-to-date, detailed specifications for the people who come after us. Have you ever met a maintenance programmer who wouldn't want a full regression test suite for the code that they're working with?
But TDD isn't perfect. Although TDD is great at specifying code at a fine-grain level, tests simply don't scale to address higher level business process and architectural issues. Agile Model Driven Development (AMDD) enables you to scale TDD through initial envisioning of the requirements and architecture as well as just-in-time (JIT) modeling at the beginning and during construction iterations. To scale requirements-level TDD, you must recognize that customer tests are very good at specifying the details, but not so good at providing overall context. High-level business process models, conceptual domain models, and use cases are good at doing so, and these work products are often created as part of your initial requirements envisioning and iteration modeling activities. Similarly, to scale design-level TDD you must recognize that developer tests are very finely grained but once again do not provide overall context. High-level architecture sketches created during envisioning activities help set your initial technical direction. During each construction iteration, you'll do more detailed design modeling to think through critical issues before you implement them via TDD.
You also need to scale the validation aspects of TDD. TDD is in effect an approach to confirmatory testing where you validate the system to the level of your understanding of the requirements. The fundamental challenge with confirmatory testing, and hence TDD, is that it assumes that stakeholders actually know and can describe their requirements. Therefore you need to add investigative testing practices which explore issues that your stakeholders may not have thought of, such as usability issues, system integration issues, production performance issues, security issues, and a multitude of others.
For further reading, I suggest:1. My article "Introduction to TFD/TDD" at http://www.agiledata.org/essays/tdd.html which overviews TDD.2. My February 2008 column in Dr. Dobb's Journal entitled "Scaling TDD" at http://www.ddj.com/architect/205207998 which explores this issue in detail. 3. Andrew Glover's article "In pursuit of code quality: Adventures in behavior-driven development" at http://www.ibm.com/developerworks/java/library/j-cq09187/ which describes a new-and-improved take on TDD called BDD.[Read More]
Agility@Scale: Strategies for Scaling Agile Software Development
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ScottAmbler 120000HESD Tags:  requirements tdd design agileadopt specification agility-at-scale amdd testing 3 Comments 6,875 Visits
ScottAmbler 120000HESD Tags:  modeling agility-at-scale agileadopt requirements 8 Comments 9,989 Visits
Contrary to popular belief, agile development teams do in fact model and yes, they even do some up front requirements and architecture modeling. Two of the best practices of Agile Modeling are Requirements Envisioning and Architecture Envisioning where you spend a bit of time at the beginning of the project doing enough initial modeling to get you going in the right direction. The strategy is to take advantage of modeling, which is to communicate and think things through without taking on the risks associated with detailed specifications written early in the lifecycle. In this blog posting I will focus on requirements envisioning, in a future posting I'll cover architecture envisioning.
The goal of initial requirements envisioning is to identify the scope of your effort. You need to do just enough modeling early in the project to come to stakeholder concurrence and answer questions such as what you're going to build, roughly how long it's going to take (give a range), and roughly how much it's likely to cost (once again, give a range). If you can get the right people together in the room, which can sometimes be a logistics challenge but not one that you couldn't choose to overcome, there are very few systems (I suspect less than 5%) that you couldn't initially scope out in a few days or a week. I also suspect that most of the remaining systems could be scoped out with less than 2 weeks of modeling, and if not then I'd take that as an indication that you're taking on too large of a project. I'm not saying that you'll be able to create big detailed specifications during this period, and quite frankly given the problems associated with "Big Requirements Up Front (BRUF)" you really don't want to, but I am saying that you could gain a pretty good understanding of what you need to do. The details, which you'll eventually need, can be elicited throughout the lifecycle when you actually need the information. A common saying in the agile community is that requirements analysis is so important for us that we do it every single day, not just during an initial phase. I'll discuss just in time (JIT) approaches to requirements modeling in a future posting.
To envision the requirements for a business application, you might want to consider creating the following models:
For small teams simple tools such as whiteboards and paper are usually sufficient for requirements envisioning. But what happens at scale? What if you're working on a large agile team, say of 50 people, 200 people (IBM has delivered software into the marketplace with agile teams of this size), or even 500 people (IBM currently has teams of this size applying agile techniques)? What if your team is distributed? Even if you have people working on different floors of the same building, let alone working from home or working in different cities or countries, then you're distributed (see my postings about distributed agile development). Suddenly whiteboards and paper-based tools (index cards, sticky notes, ...) aren't sufficient. You're still likely to use these sorts of tools in modeling sessions with stakeholders, but because of one or more scaling factors you need to capture your requirements models electronically.
In January Theresa Kratschmer and I gave a webcast entitled Agile Requirements: Collaborative, Contextual, and Correct which overviewed agile approaches to requirements elicitation and management, including requirements envisioning. We also showed how Rational Requirements Composer (RRC) can be used to electronically capture critical requirements information, enabling you to address the needs of large and/or distributed agile teams, while still remaining lightweight and flexible. I suspect that you'll find the webcast to be very illuminating and RRC something that you want to take a look at (the link leads to a trial version). Of course RRC can be used in other situations as well, but that's not what I'm focused on right now.
Teams which find themselves in regulatory environments will likely need to do more than just use RRC, as might very large teams. Regulatory compliance often requires more complex requirements documentation, which in turn requires more sophisticated tools such as DOORS or Requisite Pro, and I would consider using those tools in the types of situations that warrant it. One of the things that people often struggle to understand about agile approaches is that you need to tailor your strategy to reflect the situation at handle. One process size does not fit all, so you will end up using different tools and creating different artifacts to different extents in different situations. Repeatable results, not repeatable processes, is the rule of the day.
Agile requirements activities are evolutionary (iterative and incremental) and highly collaborative in nature. Initially requirements are explored at a high level via requirements envisioning at the beginning of the project and the details are explored on a just-in-time (JIT) basis via iteration modeling and model storming activities. The way that you perform these agile practices, and the extent to which you do so, depends on the situation in which a project team finds itself. The Agile Scaling Model (ASM) is a contextual framework for effective adoption and tailoring of agile practices to meet the unique challenges faced by a system delivery team of any size. To see how this works, let's apply the concepts of the ASM to see how we would scale our agile approach to requirements.
First, let's consider how a small, co-located team would work. The first two categories of the ASM are core agile development and disciplined agile delivery, the focus of both are small co-located teams in a fairly straightforward situation. In these situations simple techniques such as user stories written on index cards and sketches on whiteboards work very well, so the best advice that I can give is to stick with them. Some teams will take a test-driven development (TDD) approach where they capture their requirements and design in the form of executable specifications, although this sort of strategy isn't as common as it should be (yet!), likely because of the greater skill and discipline that it requires. Traditionalists often balk at this approach, believing that they need to document the requirements in some manner. But, for a small co-located team working in a collaborative manner, requirements documentation proves to be little more than busy work, often doing nothing more than justifying the existence of a business analyst who hasn't made the jump to agile yet. Don't get me wrong, there are good reasons to write some requirements documentation, and we'll see this in a minute, but you should always question any request for written specifications and try to find more effective ways to address the actual goal(s) motivating the request. Never forget that written documentation is the least effective communication option available to you.
Although inclusive tools such as whiteboards and paper work well for requirements, for development activities you will need electronic tools. You will either put together an environment from point-specific tools or adopt something more sophisticated such as IBM Rational Team Concert (RTC) which is already fully integrated and instrumented. RTC is a commercial tool, but luckily you can download a 10-license environment free of charge, which is just perfect for a small team. Larger teams, of course, will need to purchase licenses. One of the things that a disciplined agile delivery approach adds to core agile development is it addresses the full delivery life cycle, which is important because it explicitly includes pre-construction activities such as requirements envisioning. The first step in scaling agile techniques is to adopt a full delivery life cycle which covers the full range of activities required to initiate a project, produce the solution, and then release to solution to your end users.
More interesting is the third category of the ASM, Agility@Scale, and how its eight agile scaling factors affect the way that you tailor your process and tooling strategy. Let's explore how each one could potentially affect your agile requirements strategy:
ScottAmbler 120000HESD Tags:  agileadopt tdd design specification requirements testing agile 5,690 Visits
My January 2010 DDJ Agile Update, Tragic Mistakes When Adopting Test Driven Development (TDD) , is now online. In the article I summarize what I consider to be common, and tragic, mistakes that I'm seeing organizations make when they attempt to adopt TDD.
These mistakes include:
The article also goes into potential benefits of TDD as well as potential challenges that you're face when adopting it.