Predicting Test Results Without Execution

As software systems grow, test suites may become complex, making it challenging to run the tests frequently and locally. Recently, Large Language Models (LLMs) have been adopted in multiple software engineering tasks. It has demonstrated great results in code generation, however, it is not yet clear whether these models understand code execution. Particularly, it is unclear whether LLMs can be used to predict test results, and, potentially, overcome the issues of running real-world tests. To shed some light on this problem, in this paper, we explore the capability of LLMs to predict test results without execution. We evaluate the performance of the state-of-the-art GPT-4 in predicting the execution of 200 test cases of the Python Standard Library. Among these 200 test cases, 100 are passing and 100 are failing ones. Overall, we find that GPT-4 has a precision of 88.8%, recall of 71%, and accuracy of 81% in the test result prediction. However, the results vary depending on the test complexity: GPT-4 presented better precision and recall when predicting simpler tests (93.2% and 82%) than complex ones (83.3% and 60%). We also find differences among the analyzed test suites, with the precision ranging from 77.8% to 94.7% and recall between 60% and 90%. Our findings suggest that GPT-4 still needs significant progress in predicting test results.