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The emergence of using Machine Learning Techniques in software testing started in the 2000s with the rise of Model-Based Testing and early bug prediction models trained on historical defect data. It rapidly grew and began to be used for test case prioritization, defect prediction, and code analysis. Around the same time, major hyperscalers such as Google and Microsoft researched the use of AI-driven testing to optimize test execution. Other AI-powered test automation tools entered the landscape in the second half of the 2010s. Neural networks and deep learning were applied to UI testing, anomaly detection, and log analysis. Reinforcement learning also found its role in test case generation. In the last few years, self-healing test automation became the norm. Intelligent defect prediction significantly reduced testing effort by allowing ML models to predict areas of the code prone to failure. Not to mention the rise of Generative AI and its application in automated test writing, log interpretation, and debugging assistance.
But how are these techniques actually used in practice to enhance software testing? This is the topic that will be explored in this article. We will delve into the top 10 most used algorithms for quality assurance that each test engineer should know.
- Decision Trees
A decision tree is a hierarchical model that splits data into different branches based on decision rules, ultimately leading to a final classification or prediction. One drawback of Decision Trees is that they can easily overfit the training data, leading to poor generalization on unseen data. This can be mitigated by techniques like pruning, setting a maximum tree depth, or requiring a minimum number of samples per split.
For software testing, decision trees split data based on feature conditions such as lines of code, complexity, or past defects to predict whether a module will have defects. They can also be used for automated bug classification by analyzing structured data like severity and affected modules. Additionally, they can aid in test case generation by systematically analyzing decision paths derived from static code analysis or past test data to identify different input conditions and execution flows.
- Random Forest
Random Forest uses multiple decision trees to make predictions (hence the name “forest”). It aggregates the outputs of many decision trees to improve accuracy and prevent overfitting. Unlike individual Decision Trees, Random Forest reduces the risk of overfitting by averaging multiple tree predictions, making it more robust to noise in the training data.
It can help with defect prediction by identifying parts of the code more likely to have defects based on historical features such as code complexity and developer activity. Test case optimization can also benefit from Random Forest by prioritizing test cases based on the likelihood of defects, ensuring higher-risk areas are tested first. Additionally, this technique can identify areas that are not sufficiently tested by analyzing code coverage metrics, historical defect reports, and execution logs to ensure comprehensive test coverage of high-risk components.
- Gradient Boosting Machines
Gradient Boosting Machines (GBMs) is an ensemble learning technique in which decision trees are built sequentially, with each tree correcting the errors made by the previous ones. It starts with a simple model and iteratively adds new trees that focus on the errors of the existing model. Each successive tree is trained to correct the residual errors of the previous model by iteratively adjusting predictions through gradient descent.
Similar to Random Forest, GBMs can aid in defect prediction and test case optimization by identifying modules prone to defects and optimizing the order in which test cases should be executed to maximize early defect detection. Although GBMs can achieve high accuracy, they are computationally more expensive than simpler models like Decision Trees or Random Forest, making them less ideal for real-time testing applications unless properly optimized.
- Support Vector Machines
A supervised learning algorithm that works by finding the optimal boundary that best separates different classes of data, Support Vector Machines (SVM) maximize the margin between them. In higher dimensions, SVM can use kernel tricks to transform non-linearly separable data into a higher-dimensional space where a linear boundary can be applied for classification. The key concept in SVM is the use of support vectors—data points closest to the decision boundary—that determine the optimal hyperplane.
SVM can be used for defect and anomaly detection by classifying code as prone to defects or defect-free based on historical code attributes and identifying abnormal behavior in system logs or test results.
- K-Nearest Neighbors
K-Nearest Neighbors (KNN) is a simple algorithm that classifies data based on the class of its nearest neighbors. In practice, this is done by calculating the distance between a given data point and all other points in the training set and assigning the point to the class that appears most frequently among its k nearest neighbors.
In software testing, KNN can be used for test case prioritization by grouping test cases based on their similarity to those that have failed or encountered bugs. It is also useful for anomaly detection by identifying unusual behavior when comparing new observations to historical test data.
- Naïve Bayes
Naïve Bayes is a probabilistic classifier that assumes the independence of features to simplify calculations. In practice, this assumption does not usually hold, hence the “naïve” adjective. This algorithm calculates the posterior probability of each class using the prior probabilities of classes and the likelihood of the features.
Naïve Bayes can be used for bug classification by analyzing text, metadata, or historical resolution data to predict defect severity and type. It can also assist in test case prediction by forecasting which test cases are most likely to fail based on historical data and past test outcomes.
- Neural Networks
Neural networks are computational models inspired by the human brain, consisting of layers of interconnected nodes (neurons) that learn complex patterns from data. They operate by inputting data through layers of neurons, applying transformations (activation functions), and adjusting weights via backpropagation to minimize error.
Deep learning models can automate test script generation using NLP-based models for requirement analysis, RNNs for sequential test data learning, and reinforcement learning for dynamic test case exploration. Another relevant use case for neural networks is identifying complex relationships between code attributes and defect likelihood, which traditional models may struggle to capture.
- K-Means Clustering
An unsupervised learning algorithm, K-Means clustering divides data into k clusters by minimizing variance within each cluster. It initializes k centroids, assigns each data point to the nearest centroid, recalculates centroids, and iterates until convergence.
This technique can be used for test case clustering (grouping similar test cases together to optimize test execution and management) and bug categorization (clustering bug reports based on similarity to aid prioritization). A limitation of K-Means is its assumption that clusters are spherical and of similar size, which may not always hold. Alternative clustering methods like DBSCAN can be used for irregularly shaped clusters.
- Autoencoders
Autoencoders, a type of neural network, learn efficient codings of input data by compressing and reconstructing it, minimizing reconstruction error to capture normal behavior.
They can be applied to anomaly detection by identifying deviations in test execution or system logs and aiding in fault localization.
- Monte Carlo Tree Search
Monte Carlo Tree Search (MCTS) is a search algorithm used for decision-making, simulating multiple future actions to select the optimal one. It balances exploration and exploitation to refine its strategy over time.
MCTS can optimize test case execution sequences and generate test cases by simulating different execution paths.
Additional Algorithms
Other notable algorithms include XGBoost, LightGBM, One-Class SVM, Gaussian Mixture Models, DBSCAN, PCA, reinforcement learning, LSTMs, Genetic Algorithms, and Transformer-Based Models.
Machine Learning is continuously evolving, and test engineers should integrate these approaches with traditional testing methodologies rather than completely replacing them.
Conclusion
Machine Learning is continuously evolving, and test engineers should integrate these approaches with traditional testing methodologies rather than replacing them. This article aimed to demystify commonly used ML algorithms and encourage readers to explore their applications further. By understanding and leveraging these techniques, test engineers can enhance test automation, optimize defect detection, and stay ahead in today’s rapidly advancing technical landscape.
