Finite State Machine-based Testing -- Libfsmtest - An Open Source Library for FSM-based Testing -- Mining Precise Test Oracle Modelled by FSM.-Reverse-Engineering EFSMs with Data Dependencies -- Testing against non-deterministic FSMs: a probabilistic approach for test suite minimization -- Test Generation and Selection -- Automatic test generation with Asmeta for the Mechanical Ventilator Milano controller -- Locality-based Test Selection for Autonomous Agents -- Improving model inference via W-set reduction -- Using Ant Colony Optimisation to Select Features having Associated Costs -- Initial Results on Counting Test Orders for Order-Dependent Flaky Tests using Alloy -- Metamorphic Testing of Logic Theorem Prover -- AI-based Techniques -- Creation of Human-friendly Videos for Debugging Automated GUI-Tests -- Combining Holistic Source Code Representation with Siamese Neural Networks for Detecting Code Clones -- Robustness Analysis of Deep Learning Frameworks on Mobile Platforms -- Use Cases -- Specification and validation of numerical algorithms with the Gradual Contracts Pattern -- Solving the instance identi cation problem in micro-service testing -- On the Quality of Network Flow Records for IDS Evaluation: a Collaborative Filtering Approach -- GROOT: A GDPR-based Combinatorial Testing Approach -- APPENDIX Project Reports -- H2020 DIGITbrain Advanced Digital Twins for Manufacturing -- Definition and Assessment of Security and Service Level Agreements -- Attack configuration Engine for 5G networks -- The BIECO Conceptual Framework Towards Security and Trust in ICT Ecosystems -- Industrial Machine Learning for Enterprises (IML4E) -- NLP-based Testing and Monitoring for Security Checking.

This book constitutes the refereed proceedings of the 33rd IFIP WG 6.1 International Conference on Testing Software and Systems, ICTSS 2021, which was supposed to be held in London, UK, but was held virtually due to the COVID-19 pandemic. The 10 regular papers and 7 short papers presented were carefully reviewed and selected from 36 submissions. Additionally, the volume includes 6 project reports. The papers are divided into the following topical subheadings: Finite State Machine-based Testing; Test Generation and Selection; AI-based Techniques; Use Cases; Project Reports.