Test Amplification for REST APIs via Single and Multi-Agent LLM Systems

Abstract: REST APIs (Representational State Transfer Application Programming Interfaces) are essential to modern cloud-native applications. Strong and automated test cases are crucial to expose lurking bugs in the API. However, creating automated tests for REST APIs is difficult, and it requires test cases that explore the protocol's boundary conditions. In this paper, we investigate how single-agent and multi-agent LLM systems can amplify a REST API test suite. Our evaluation demonstrates increased API coverage, identification of numerous bugs in the API under test, and insights into the computational cost and energy consumption of both approaches.