Test-Driven Development (TDD) for AI Agents
Dan O'Riordan
VP AI & Data Engineering : Agentic Engineering is where we are going so buckle up...
Test-Driven Development (TDD) is a software methodology where tests are written before implementing functionality. In AI development, this approach is gaining traction to improve response accuracy, reliability, and robustness. Below, we explore case studies of TDD in AI, best practices, evaluation metrics, research insights, and guidance for real-world applications. Each section provides actionable insights with supporting references.
1. Case Studies: TDD in AI Development
Casetext’s Legal AI (Co-Counsel): An illuminating case is Casetext’s AI legal assistant. Founder Jake Heller stressed that while he wasn’t a TDD advocate in general software, TDD was “10x more important” when building with Large Language Models (LLMs) In the high-stakes legal domain, Heller’s team created a comprehensive test suite and iteratively refined the AI’s prompts until it achieved near-perfect accuracy They aimed for 100% accuracy before deployment, knowing even small errors could erode user trust in legal practice This test-first approach allowed Co-Counsel to meet the exacting standards of lawyers, contributing to Casetext’s success and eventual $650M acquisition
OpenAI and Systematic Evaluations: OpenAI has adopted a similar ethos by releasing the OpenAI Evals framework, enabling developers to define evaluation tasks (tests) for model responses. For example, Azure’s OpenAI Service evaluation allows testing models against expected input/output pairs to assess performance on accuracy and reliability before deployment (How to use Azure OpenAI Service evaluation - Azure OpenAI | Microsoft Learn) (How to use Azure OpenAI Service evaluation - Azure OpenAI | Microsoft Learn) This means teams can predefine prompts and expected answers as “unit tests” for an AI model, catching inaccuracies or unwanted behaviors early. Such frameworks illustrate how leading AI firms treat evaluation as an integral part of development, akin to TDD.
Other Industry Examples: Numerous organizations are incorporating TDD for AI:
·????? ThoughtWorks & GitHub Copilot: ThoughtWorks noted that combining TDD with practices like pair programming can harness AI coding assistants more safely By writing tests for generated code, developers ensure Copilot’s suggestions meet the intended functionality and quality.
·????? MLOps in Enterprises: Companies deploying ML at scale (e.g., in finance or healthcare) often require test harnesses around models. For instance, IBM’s best practices for AI include writing tests for data integrity and model behavior as part of their AI validation toolkit Google’s internal ML platforms similarly emphasize testing data preprocessing and model outputs to prevent training-serving skew and regressions (Test-Driven Machine Learning - InfoQ)
·????? Autonomous Systems: Self-driving car development teams use simulation to practice TDD. For example, engineers at Tesla and Waymo design virtual driving scenarios as test cases (e.g., a pedestrian jaywalking) and then improve the driving policy until the test scenario passes. This scenario-based TDD for autonomy helps catch safety issues in simulation before real-world trials
Key Takeaway: Across industry cases, teams implementing TDD for AI report higher reliability and user trust. By defining expected outcomes first and insisting the AI meets them, organizations like Casetext achieved impeccable accuracy in critical applications The case studies underscore that TDD is feasible and valuable in AI – from LLM-powered assistants to autonomous vehicles – especially when mistakes carry significant risk.
2. Best Practices for Implementing TDD in AI
Applying TDD to AI requires adapting traditional test-first principles to the nuances of machine learning and data-driven behavior. Below are best practices, methodologies, and tools for effective TDD in AI:
o?? Natural Language Unit Tests: Tools like LMUnit by Contextual AI enable writing tests in plain English to check qualities of LLM outputs These are essentially assertions about the response (e.g., “Does the answer cite a source for factual claims?”). LMUnit’s model can automatically score an AI’s output against these criteria, integrating with CI/CD for continuous feedback This approach maintains software engineering rigor while allowing non-engineers to contribute test cases in natural language
o?? OpenAI Evals / Promptfoo: These frameworks allow you to specify prompt + expected answer pairs or quality criteria and then automatically run your model against them. They facilitate a test-driven prompting approach: you write an eval (test), see the model fail, then adjust your prompt or model and repeat until it passes. This was crucial in refining prompts for Co-Counsel’s legal AI
o?? Metamorphic Testing: Because AI functions (especially ML models) don’t always have a single correct output, metamorphic testing is valuable. In metamorphic testing, you define relationships between inputs and outputs rather than exact answers. For example, if an image’s brightness is increased, a vision system should still consistently identify objects (the specific pixel outputs may differ, but e.g., object count should remain the same). Metamorphic tests are well-suited for ML because they bypass the lack of a strict oracle Tools and libraries (e.g., Giskard or Lakera for ML testing) can help implement such property-based tests to ensure model behavior changes predictably under transformations.
o?? Traditional Testing Frameworks with ML Extensions: Standard testing frameworks like PyTest or unittest can still be used to structure AI tests. You can write unit tests for data preprocessing functions, model interface contracts, etc. Additionally, libraries such as Great Expectations help in TDD for data – you can enforce expectations (tests) on data quality (schema, distributions) so that any anomaly in input data triggers a test failure before it impacts the model in production.
o?? Use CI/CD: Continuous integration should run AI tests (including model inference on test cases) whenever changes are made. LMUnit’s design explicitly supports this by plugging into pipelines for real-time feedback
o?? Track versioned metrics: Store historical test results and evaluation metrics for each model version to catch regressions. For example, if a new model version improves overall accuracy but starts failing some previously passed edge-case tests (like responding incorrectly to a rare query), the pipeline should flag it.
o?? Encourage a “failing test culture”: It should be normal that if an evaluation fails, the model isn’t ready to ship. This mindset shift – similar to traditional TDD – ensures higher reliability. For instance, Heller’s team refused to launch the legal AI until all tests (questions) were answered correctly underscoring a zero-tolerance approach to known errors in critical AI outputs.
By adopting these practices, teams can build AI systems that are robust by design. TDD encourages thinking upfront about how the AI should behave, leading to better design decisions and fewer surprises after deployment. The use of specialized tools (LMUnit, OpenAI Evals, CheckList, etc.) further streamlines this process, making TDD scalable even as models and datasets grow.
3. Evaluation Metrics and Benchmarking Strategies
A core aspect of TDD for AI is defining how to measure “accuracy, reliability, and robustness” of model responses. Traditional metrics provide a starting point, but AI often requires more nuanced evaluation. Here we outline key metrics and benchmarking strategies:
o?? Accuracy: Percentage of correct outputs (e.g., correct class labels or answers). Applicable in scenarios with a ground-truth reference.
o?? Precision & Recall: For tasks with class imbalance or open-ended outputs (like information retrieval or anomaly detection), precision and recall (and F1 score) are critical to quantify false positives vs.?false negatives.
o?? ROC/AUC: In binary classification or risk scoring (like a fraud detection AI), ROC curves and AUC capture the trade-off between sensitivity and specificity at various thresholds.
???????????????? TDD in such contexts means writing tests expecting the model to achieve at least certain metrics on a validation set. For instance, a test might assert that “the model’s F1 on intent recognition must be ≥ 0.90 on the test suite,” failing the build if not met.
o?? Coherence and Relevance: For conversational AI, use metrics that gauge if responses stay on topic and make sense in context. This could be as simple as a human-rated coherence score or as structured as BLEU/ROUGE for checking overlap with reference answers (common in summarization or translation tasks).
o?? Diversity & Creativity: If an AI agent generates recommendations or creative content, you might measure diversity (e.g., diversity of recommended items, or lexical diversity in generated text).
o?? Factual Accuracy: For knowledge-based agents, metrics like fact-check accuracy or a score from an information retrieval eval can quantify correctness. For example, you could compare the AI’s answer to a database and score it 1 if it matches the verified truth, 0 if not (a simple accuracy, but on a custom set of factual queries).
o?? Robustness Metrics: To gauge reliability, robustness tests examine model performance under perturbed conditions. For NLP, this might be accuracy under input paraphrases, or resilience to minor spelling errors. For vision, it could be classification accuracy with various image transformations (blur, brightness changes). A robust AI would have minimal performance drop on these altered inputs. You can define a metric like “relative accuracy under stressors” and require it above a threshold.
o?? It identifies specific failure modes (e.g., the model fails negation tests or misclassifies all inputs mentioning a certain rare term).
o?? It gives actionable insight on what to fix, which is perfect for test-driven improvement.
o?? The OpenAI Evals platform and Azure’s evaluation tool allow automated benchmarking on custom datasets (How to use Azure OpenAI Service evaluation - Azure OpenAI | Microsoft Learn) These tools often output a report of accuracy and other metrics for each eval run, enabling easy comparison between model versions or different models.
o?? Academic benchmarks (like GLUE for NLU, COCO metrics for image captioning, etc.) provide standard test sets. Integrating these into your pipeline (with tests asserting your model meets or exceeds state-of-art on specific tasks) can be part of TDD goals, especially for research-driven development.
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o?? Leaderboards and Competitions: In some cases, you might use public leaderboards as external benchmarks (though not exactly TDD, they help gauge reliability relative to others). But more directly, frameworks like LangChain’s evaluation module or PromptGPT allow creating assertions on LLM outputs, effectively turning benchmarks into tests that can run in CI.
In summary, defining the right metrics is integral to TDD for AI. You must decide what “correct” means for your agent – whether it’s an exact answer match, an above-threshold BLEU score, or satisfying a checklist of requirements. TDD then means the AI is not done until it meets all those metrics and tests. This approach ensures accuracy (measured by domain-appropriate metrics) and reliability (consistent performance across scenarios) are baked into the development process, rather than evaluated as an afterthought.
4. Research and Industry Insights on TDD in AI
The intersection of TDD and AI is an evolving field, with contributions from both academia and industry. Here we highlight notable research papers, frameworks, and expert insights that shed light on using TDD in AI development:
In summary, research and industry sources converge on the notion that proactive testing significantly enhances AI reliability. Whether through formal test cases, behavioral checklists, or continuous evaluation, the evidence shows that treating AI development like regular software engineering – with rigorous TDD – yields more trustworthy models These insights provide both justification and guidance for AI teams to invest in TDD practices.
5. TDD Implementation Guidance for Real-World AI Applications
Implementing TDD for AI agents can vary by application domain. Below we provide guidance and examples for three common areas: conversational AI, autonomous systems, and recommendation engines. The goal is to illustrate how TDD can be practically applied to improve system accuracy and robustness in each context.
TDD for Conversational AI (Chatbots & Virtual Assistants)
Approach: Treat each possible dialogue or query as a test case. Start by defining conversation scripts and user intents that the system must handle. For each: - Write an expected response (or set of acceptable responses) for a given input. For example, a customer support chatbot might have a test: Input: “My internet is slow and keeps disconnecting.” Expected: The bot should apologize and provide troubleshooting steps (and not give a generic or off-topic answer). - Include variations of the input as additional tests: typos (“internnet is slo…”), slang or different phrasings (“my wifi is acting up”), and even unrelated or malicious inputs to ensure the bot responds safely (“You are stupid” – expected: a polite deflection or adherence to policy).
Execution: Use a framework to run the bot against these tests. OpenAI’s evals or custom test harness code can simulate a user message and capture the bot’s reply to compare against expected output. Alternatively, use a specialized conversational testing tool (some exist to test Alexa/Google Home skills via scripts).
Iteration: When a test fails (e.g., the bot gives a wrong or unsatisfactory answer), apply fixes: - If using a retrieval-based or modular bot, perhaps the NLU misclassified the intent – you might refine the training data or rules and then rerun the tests. - If using an LLM-based bot, you might adjust the system prompt or few-shot examples to better steer the response. For instance, if the bot responded to a billing question with a non-answer, add a few-shot example of a correct billing query response to the prompt, then test again.
Gradually expand your test suite to cover more dialog turns (multi-turn conversations). For example, a multi-turn test: user asks a question, bot answers, user asks a follow-up – you expect the bot to maintain context. These can be implemented as sequential assertions in your test. Ensuring all such tests pass means the bot can handle context and follow-ups reliably.
Tools & Best Practices: Keep tests short and focused on one behavior (just like unit tests). Leverage any conversation simulator provided by the platform (e.g., for Alexa skills, the ASK toolkit allows automated utterance tests). Additionally, incorporate live testing feedback: if real users stump the bot with a new query, add it (with the desired answer) to the test suite so the bot learns to handle it in the next iteration. Over time, this yields a conversational agent with a wide coverage of user scenarios and a proven track record of correct responses before they even go live.
TDD for Autonomous Systems (Self-Driving Cars & Robotics)
Approach: In autonomous systems, simulation is your testing ground. TDD can be applied by writing scenario tests: - Define a scenario and expected outcome. For example: Scenario: A pedestrian crosses unexpectedly 40 meters ahead of the self-driving car traveling at 40 km/h. Test Expectation: The car should decelerate and come to a complete stop before the crosswalk, avoiding the pedestrian, with no collision. - Scenarios can be coded in simulation engines (such as CARLA or LGSVL for driving, or Gazebo for general robotics). The test is essentially running the sim with the AI agent controlling the vehicle/robot and checking if safety constraints are met (no collisions, obey traffic law, etc.).
Execution: Initially, many scenarios might “fail” (the agent doesn’t behave as desired). Under TDD, you’d write the failing scenario first – e.g., a complex intersection with an ambivalent traffic light – observe the failure (agent incorrectly proceeds), then improve the agent: - If rule-based logic, code the fix (e.g., improve how the state machine handles yellow lights). - If ML-based (like a policy network or planning module), perhaps add training data for that case or adjust reward functions, then re-test.
Iteration: Keep adding scenarios incrementally: - Start with basic ones (car follows lane, stops at red light). - Add complexity (construction zone, merging traffic, erratic driver cutting in, etc.). - Each scenario is analogous to a unit test. Only when all simpler scenarios pass, move to more complex integrations (like an end-to-end drive through a city). This prevents regression in basic driving skills while adding new capabilities.
Metrics & Automation: For each scenario test, define quantitative pass criteria: e.g., “no collision and car stops within X meters” or “robot arm grasps object within 5 seconds with >90% grasp stability.” These criteria make the test objective (pass/fail). Modern autonomous vehicle development uses thousands of simulated miles as test cases; University of Michigan researchers managed to reduce required real miles by 99% through intelligent AI-driven testing – essentially finding the important test scenarios through AI, then using them to validate the system Incorporating those scenarios via TDD ensures the autonomous system is exposed to edge cases in simulation rather than on the road.
Deployment Testing: Even after simulation, do staged rollout with TDD principles: e.g., in a closed course, then limited real environment. Treat any unexpected event on the road as a new test to write for the simulator. This continuous loop hardens the agent. The mantra in autonomous systems is “if it’s not tested, it’s not safe.” TDD enforces that by requiring a test (scenario) for every safety or performance requirement from day one.
TDD for Recommendation Engines (Personalization Systems)
Approach: Recommendation systems are often evaluated on aggregate metrics (like click-through rate or purchase rate in A/B tests). TDD complements this by ensuring the system meets certain behavior expectations on a per-case basis, before live deployment: - Identify key use cases and user stories for recommendations. For example: New user with no history should get a diverse set of popular items. Or User who mainly watched science-fiction movies should see sci-fi recommendations, not random genres. Each of these can be a test case. - Create synthetic user profiles or sessions that reflect these scenarios. For a new user, an empty history; for the sci-fi fan, a history of sci-fi movies rated highly.
Execution: For each user profile test case, run the recommendation algorithm offline (in a test environment) to get the top N recommendations. Then check the results against your criteria: - Does the new user get a variety of generally popular or trending items? (If the system returns niche content, that might fail the test for diversity.) - Does the sci-fi fan’s top 5 contain at least, say, 3 sci-fi titles? If the test expects genre alignment and the results violate that (e.g., all recommendations are comedy movies), mark it as fail.
Use of RecList: The RecList library provides a structure to implement such tests systematically ([2111.09963] Beyond NDCG: behavioral testing of recommender systems with RecList) It allows you to define expected behaviors for different recommendation “slices” (segments of users or content) and automatically evaluate the model. For instance, RecList could test a music recommender to ensure that if a user has listened only to classical music, the recommendations aren’t suddenly hip-hop – unless some diversity is intentionally expected and controlled. RecList’s methodology, as described by Chia et al., is to treat each behavioral expectation as a testable component, much like unit tests in software ([2111.09963] Beyond NDCG: behavioral testing of recommender systems with RecList)
Iteration: When a recommendation test fails: - Analyze whether it’s the model (e.g., a collaborative filtering system might overly favor popular content, failing niche personalization tests) – in which case, adjust the algorithm or add constraints (like ensure a certain diversity quotient in results). - It could also be data issues (maybe the user profile data wasn’t properly processed). TDD will surface these problems early, allowing a fix (e.g., fix the feature pipeline that wasn’t recognizing the user’s genre preferences correctly). - After adjustments, run the tests again and ensure all pass before considering deployment or further tuning.
Metrics and Benchmarks: In addition to behavioral tests, ensure the algorithm meets baseline metrics on historical data (e.g., at least the same hit-rate or mean reciprocal rank as the previous model on a test set). TDD for recommenders thus includes both “hard” checks for specific scenarios and aggregate metric checks. Together, they ensure not only overall performance but also that critical use cases are handled correctly.
Real-World Scenario: Suppose a recommendation engine at an e-commerce site is being updated. A TDD approach would involve writing tests like: - “If a user bought baby diapers last week, the system should recommend baby products (wipes, formula) and not unrelated items.” – Then verify the new model’s recommendations for a mock profile that has diapers in purchase history. - “A user who frequently views vegan recipes should see predominantly vegetarian/vegan dish recommendations, not a feed full of steak recipes.” – Test with a sample user data reflecting that behavior. By enforcing these domain-derived rules in tests, developers encode business logic and ethical considerations (like not showing inappropriate content) directly into the development cycle.
Putting It All Together: Implementing TDD for AI agents means merging data science with rigorous software engineering discipline. It requires effort to create and maintain test datasets and evaluation code. However, the payoff is significant: higher accuracy, more reliable and debuggable models, and faster iteration once the test framework is in place. As seen in the case studies, teams that embraced TDD for AI (like Casetext in legal AI) achieved remarkably robust systems that gained user trust By following best practices, using the right tools, and continually measuring via well-chosen metrics, any AI development team can improve the accuracy, reliability, and robustness of their agent’s responses.
References:
·????? Heller, J. (Casetext) – Emphasis on test-driven approach for legal AI
·????? NextBigWhat on Vertical LLMs – Importance of 100% accuracy in high-stakes AI
·????? Azure OpenAI Service – Using evals to test models on expected I/O for accuracy and reliability (How to use Azure OpenAI Service evaluation - Azure OpenAI | Microsoft Learn) (How to use Azure OpenAI Service evaluation - Azure OpenAI | Microsoft Learn)
·????? Akira AI – TDD for LLMs and need for customized evaluation metrics
·????? Ribeiro et al.?(2020) – CheckList: behavioral testing for NLP models
·????? Chia et al.?(2022) – RecList: testing recommender systems beyond simple metrics ([2111.09963] Beyond NDCG: behavioral testing of recommender systems with RecList)
·????? Contextual AI – LMUnit: natural language unit testing enabling TDD for AI systems
·????? Metamorphic Testing for ML – Concept of testing transformations when exact expected output is unknown
·????? InfoQ (Detlef Nauck) – Importance of testing data and ML models for reliable predictions
Founder consultant at Cloud Bastion with expertise in Automotive sector, Software Development Management and Information Security
2 周Thanks for interesting thoughts summarized in a great and article Dan! With all the many embarrassing AI failures we have seen recently, your post is very timely and one wonders if software testing is sometimes completely forgotten in the current AI excitement. Also some great references at the end! I have been involved in several automotive projects with complex AI models where the test results are not black and white. This experience confirms that what you refer to as accuracy is very important. Here statistics, KPIs and databases of complex excluded corner cases are used to determine when the complex system is good enough. Be prepared to spend lots of time on discussing and understanding this topic with domain experts, developers and customer management! Yes, the involvement of domain experts in testing is crucial. I specialize in getting projects back on track and, as shocking as it might seem, one of the first measures is often to find and involve domain experts. My key recommendation for AI agent test planning is that some errors may take a long time to fix: I am referring to the problems which call for time consuming collection of new training data and regeneration of a big LLM. Thanks again for a great article!
Android Developer Kotlin and Java with over 5 years of commercial development experience. More than 20 years of overall engineering expertise.
3 周Insightful
Love this- TDD is being used a lot but this is the first long post I’ve seen on the topic
PhD | AI and People Lead | End-to-End GenAI Solution Implementation
1 个月Dan! I am looking forward to reading your article after we successfully push one agentic GenAI app to UAT today! I've been wanting to write an article on the difference between a GenAI POC and a proper scalable GenAI app for months. I will probably ask LLM to summarise your article first :D
CIO Europe & Global head, Technology Strategy, WIPRO
1 个月Very informative and great coverage Dan. Honestly read only first 5 pages thus far, promised to myself that will finish the rest before the weekend.