A guided path for TDD

• What is testing? - Discover what a test is from the perspective of a practitioner and the different shapes that are out there to distribute the different types of tests from the point of view of TDD
• Should you test? - In this section there is a discussion about testing or not and its benefits are discussed. More specifically on the automation part of it
• A gentle introduction to TDD - TDD is introduced as a methodology and describes its different flavors
• Is TDD testing? - The debate about testing or not is up for TDD as well, this section dives into the subject.
• The many types of tests in software testing - Integration? End-to-end? Acceptance? Let’s see how they fit from a testing point of view
• The differences between frontend and backend - Tips that are hidden from practitioners’ point of view writing tests for client and server applications.

• An approach to improve the TDD flow
• How to approach testing as a person in the software industry

• An report on experience

Learning Test-Driven Development is one of the most challenging topics for practitioners, randing to creating the test scenario that reflects reality to the maintainability of the source code. In this section we will see the different aspects of TDD and how to approach them focused on the learning aspect of it. We start with tools and then we focuses on the hands-on part of it.

• Tooling: Frameworks available for testing
  • PHPUnit
    • PHPUnit coverage on vagrant
  • Jest
    • Jest asserts beyond equals - tips for improving assertions
    • Jest timers and ReactJs - How to use jest time-related functions
  • Vitest
  • Jasmine
  • Junit
• The learning path
  • Katas - why, when and how
    • The usage of katas requires a proper setup in the programming language of choice, this is were the community repositories come into play.
      • https://github.com/SoftwareCraftersMurcia/kata-setup
      • https://github.com/swkBerlin/kata-bootstraps
      • https://github.com/codurance/katalyst-kickstart
  • Learning process of TDD from 0 to proficient - Last accessed: 29 March, 2025
    • A guided journey curated with 6 levels that, starting with the basics and ending with architectural patterns. It goes into related subjects such as SOLID and design patterns
  • TDD learning path - a broader approach to TDD with, SOLID and legacy code - Last accessed: 29 March, 2025
    • A curated set of materials about TDD with surrounding subjects such as SOLID and legacy code

Test doubles are the basis of the automated testing practice, in this section we will see the different types of test doubles and how to use them in the context of TDD.

• The history
• Mocks, dummies, spies, fakes - testing your code
• Are true mocks evil?
  • Using Fakes for testing

• On one hundred percent code coverage - how to approach coverage and void misusing it
• TDD anti-patterns - The liar, excessive setup, the giant, slow poke
• TDD anti-patterns - The mockery, the inspector, the generous leftovers and the local hero
• TDD anti-patterns - The nitpicker, the secret catcher, the dodger and the Loudmouth
• TDD anti-patterns - The greedy catcher, The sequencer, Hidden dependency and The enumerator
• TDD anti-patterns - The stranger, The operating system evangelist, Success against all odds and The free ride
• TDD anti-patterns - The One, The Peeping Tom, The Flash and The Jumper

• The hexaghonal architecture

• Rethinking legacy code and testing
• Retrofitting Tests into a ReactJS Codebases without tests

• Reduced numbre of defects
  • How effective is test-driven development?
    • Study first found from: Munir, H.; Moayyed, M.; Petersen, K. Considering rigor and relevance when evaluating test driven development: A systematic review. Inf. Softw. Technol. 2014, 56, 375–394.
  • Bissi, W.; Serra Seca Neto, A.G.; Emer, M.C.F.P. The effects of test driven development on internal quality, external quality and productivity: A systematic review. Inf. Softw. Technol. 2016, 74, 45–54
    • It examines articles published from 1999 to 2014.
    • The analysis shows 76% of studies found TDD significantly boosts internal quality and 88% noted improvements in external quality.
      • external quality is defined as:
        • Defect Density: This is often evaluated through black box testing, where the number of test cases that pass or fail indicates the stability and reliability of the software.
        • User Experience: This includes factors such as usability, performance, and the software’s ability to meet user expectations and requirements effectively.
      • However, it also reveals mixed results for productivity—particularly a drop in industrial settings.
  • Rafique, Y.; Miši´c, V.B. The Effects of Test-Driven Development on External Quality and Productivity: A Meta-Analysis. IEEE Trans. Softw. Eng. 2013, 39, 835–856
    • TDD shows a small positive impact on code quality but minimal effect on productivity.
    • Industrial studies indicate a greater decline in productivity compared to academic ones.
    • Factors like developer experience and task size play significant roles in quality improvement.
  • Benato, G.B.; Vilela, P.R.S. Test-Driven Development: Uma revisão sistemática. Rev. Bras. Comput. Apl. 2021, 13, 75–87
    • Test-Driven Development (TDD) results in a reduction in the number of defects found in the most advanced phases of software development. Specifically, it has been found that the use of TDD allows a 50% improvement in the defect rate of functional system tests, as analyzed in a study by Maximilien and Williams (2003).
  • Desai C, Janzen D, Savage K. A survey of evidence for test-driven development in academia. ACM SIGCSE Bulletin. 2008 Jun 1;40(2):97-101
    • TDD presents a potential solution to enhance software testing skills among students
    • Quality of Code: Most controlled experiments comparing TDD with other testing practices indicate an improvement in code quality. The results show a reduction in defects by approximately 35% to 45%. This is attributed to the practice of writing tests before developing code, which forces programmers to consider functionality and necessary conditions early in the development process, leading to better design decisions
    • Student Productivity: The impact of TDD on productivity varied among studies. Some experiments reported significant increases, with productivity improvements ranging from 24.5% to 50%. However, there were also studies that observed minimal or even negative effects on productivity, showing reductions between 5% and 10%
    • Increased Confidence and Understanding: Surveys conducted with students indicated that TDD contributes to greater program understanding and confidence in their coding abilities
  • Lui, K.M., Chan, K.C.C. (2004). Test Driven Development and Software Process Improvement in China. In: Eckstein, J., Baumeister, H. (eds) Extreme Programming and Agile Processes in Software Engineering. XP 2004. Lecture Notes in Computer Science, vol 3092. Springer, Berlin, Heidelberg
    • Software Quality: TDD has been shown to improve software quality by reducing the number of defects and accelerating defect resolution. Data collected revealed that teams using TDD could fix defects significantly faster than those not using it, producing fewer defects overall. For example, TDD teams fixed 97% of defects within one day versus 73% for non-TDD teams
  • Realizing quality improvement through test driven development: results and experiences of four industrial teams
    • Teams at Microsoft and IBM adopted TDD, resulting in a significant reduction in pre-release defects, by 40% to 90%.
    • The study emphasizes TDD as a vital part of agile methodologies and aims to provide empirical insights into its effectiveness.
  • Effectiveness of Test Driven Development and Continuous Integration – A Case Study
    • Increased Defect Discovery: The first project (CS1) had 414 viable bug reports, while the second project (CS2), which utilized TDD and CI, had 474 viable bug reports. This indicates a higher number of defects were found in CS2 compared to CS1
  • Comparing the Defect Reduction Benefits of Code Inspection and Test-Driven Development
    • code inspection is generally more effective at identifying defects, while TDD promotes early bug detection and better design practices, but with more variability in its effectiveness and potentially higher development time.
  • Effects of Test-Driven Development : A Comparative Analysis of Empirical Studies
    • Most industrial studies found that the intervention had a positive impact on reducing defects. In some cases, the improvements were substantial compared to the company’s previous performance levels.
• Improved code design
  • Does Test-Driven Development Really Improve Software Design Quality?
    • Emergent Design: TDD enables design to evolve through short, iterative cycles of writing tests and code. This approach allows developers to refine their designs continuously, leading to a more adaptable architecture
    • Modularization: TDD encourages developers to create smaller, more focused units of code. This modularization improves the manageability of the codebase and facilitates easier maintenance and understanding
• Reduced Technical Debt
  • Reducing Technical Debt with TDD and BDD Practices in CI/CD
    • The initial technical debt ratio for both teams was 0.45, indicating a moderate level of technical debt. After six months of practicing TDD and BDD, it reduced to 0.31 for Team A and 0.29 for Team B.