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Test-Driven Development (TDD)

In recent years, there’s been a lot of buzz surrounding the TDD methodology and its actual effectiveness in real-world application. While there is interest surrounding test-first development, some teams are still “on-the-fence” in determining whether or not the time it takes to adopt, train and oversee the TDD process is worth it.

We’ve been in this business for a long time, working on many different types of projects for many different types of organizations and seeing development trends come and go. The fact of the matter is Test-Based Development has definitely been proving itself. In just the past few years, we’ve been seeing more and more businesses start to shift their focus to agile technologies and test-based practices as the primary modus operandi for developing of complex, high-performance systems.

For an interesting and efficient way to get up to speed on TDD, watch this video. The Test-Driven Development for Complex Systems Introduction answers What exactly is TDD?, Why should I adopt TDD? and How do I apply TDD on complex systems?.


What is TDD?

Test-Driven Development, or TDD, is a quality-focused, advanced object-oriented software development methodology widely used within the Agile community. In this test-first approach programmers create automated unit tests before writing the production code. What makes TDD unique is its focus on design specification rather than validation. The TDD approach leads to higher quality software architecture by improving quality, simplicity, and testability while increasing code confidence and team productivity.

When implementing a TDD approach, the tests used are comprised of true and false assertions that indicate correct behavior when the test is passed. Writing the tests first not only helps measure the testability of the application itself but also forces the developer to concentrate on the advanced design concept from the very beginning. By developing a set of functional test cases first, developers can be assured that:

  • » Newly implemented features work as expected.
  • » The associated modifications to the code base did not break existing behavior.
  • » The software is always in a healthy state or at least vocal about the ways it might be defective.

For TDD, a unit is most commonly defined as a class or group of related functions, often called a module. Keeping units relatively small provides critical benefits, including:

  • » Reduced Debugging Effort – When test failures are detected, having smaller units aids in tracking down errors.
  • » Self-Documenting Tests – Small test cases have improved readability and facilitate rapid understandability.

Essentially, the methodology of TDD is to ensure that not only the functional code is a success but also that the test itself actually works.

This great Infographic outlines the basics of TDD.

Test Driven Development Infographic

Click for full Infographic.

The TDD Micro-Cycle: Red – Green – Refactor

The driving philosophy of TDD is “Red-Green-Refactor” which is an iterative development micro-cycle in which the tests and behavior are implemented.  First, newly written test cases test the unwritten code and as such fail (Red).  Once the developer implements the feature in the simplest manner, the corresponding tests should pass (Green).  Before starting with the next feature developers refactor their code for clarity and simplicity, with confidence provided by the ability to rerun the previously implemented test (Refactor). By adopting this red – green – refactor mantra, the developer’s production code evolves to a higher level of streamlined communication, confidence, and overall productivity.

The TDD micro-cycle provides rapid feedback to the developer: as soon as a code change is completed, it is tested. If the code has an error, it is instantly caught. The immediacy and locality of the feedback is very valuable. An effective micro-cycle requires quick compilation and execution of test cases. This requirement is central to sustaining the pace of development and reducing the obtrusiveness of tests. A key technique is to enable the automatic execution of test cases as a post-build activity, which combines building and testing into a single developer step. This technique reduces manual steps and blends building and testing into one coordinated activity.

Click to zoom.

The basic steps of TDD are easy to learn, but the mindset may take a bit of getting used to:

  • Step #1- Create/add a new test.
  • Step #2- Run the test to ensure that it fails.
  • Step #3- Write just enough code so that the test will pass.
  • Step #4- Refactor the new code to remove duplication and unnecessary complication.
  • Step #5- Ensure that refactoring did not break the code under test.
  • Step #6- Repeat this process until all tests have been written and passed.

Why TDD?

Like any other development methodology, TDD requires a shift from code-focused paradigms to a test-based approach. While adopting a Test-Driven Development approach takes significant effort and may subject a development organization to the pain of culture change, the benefits can far outweigh these costs. This shift improves system quality and reliability, maximizes developer productivity and significantly speeds time to market. Ultimately, the most significant business gains delivered by TDD come from substantially and fundamentally boosting the quality of the software components of your system. A few key benefits are highlighted below:

Improves Quality

The TDD approach forces each component to steadily build capability at a consistently higher level of quality by testing first, developing in small increments, and requiring tests to pass. Once individual component development switches to integration, this high level of component quality leads to rapid integration and more effective testing. The effort to build a broad base of automated tests incrementally throughout the development cycle yields a far more complete and valuable base of tests than a rushed, and often truncated, test effort at the end of the project. Throughout the development lifecycle the increased focus on testing helps maintain a higher focus on quality in general. This continual investment in quality yields significant dividends at the overall system level.

Promotes Simplicity

During the implementation of a feature, the test-driven developer writes the simplest code to make the tests pass.  TDD helps developers avoid over-engineering solutions due to its short development micro-cycle. It also helps break the problem into modular units and produce a solution that can be tested as well as implemented. This approach to development has the effect of simplifying code design and achieving the associated benefits, including improved readability and understandability. The more complex the problem, the more important it is to ensure each unit is coded in as simple a manner as possible.

Cuts Time-to-Market

The TDD cycle is shorter than the traditional development cycle. By focusing on building only what is needed to get the tests to pass and using immediate feedback to reduce regression errors, the development cycle can quickly be reduced to its essential core. Quality improvements gained at the component level speed development of the component itself and also slash the time needed to integrate components into the complete system by a substantial degree. Typically, integration delays for systems with average component quality will bloat software development and delivery schedules.  When applying a TDD approach instead, most component issues are resolved much earlier in the process or eliminated outright, thus shrinking integration times and quickly getting the completed product to market.

Enhances Flexibility

Current realities driving business in the realm of high-performance software include tightening competition, reduced schedules, and tighter market windows. Opportunities do not wait for convenient times to emerge – they must be seized immediately. TDD boosts a software development organization’s ability to rapidly respond to changing requirements or unanticipated product updates by facilitating shorter development and integration cycles and supporting the rapid refinement of new requirements. A solid TDD culture with a rich test base is the best preparation to rapidly seize opportunities and beat competitors to market.

Rapidly and effectively bring your team up to speed with proven techniques in TDD with Pathfinder Solutions’ Effective TDD training and Expert TDD mentoring. Contact us to learn more.