Generating Test Inputs and Interactions with the Fandango Fuzzer: How to Test Complex Systems Automatically and Exhaustively

Abstract

Even in the age of AI, generating comprehensive test inputs for software systems remains a challenge, particularly for interactive and reactive systems, which require entire interaction sequences to reach the desired states or to cover missing behavior. While modern fuzzers are effective at generating random inputs that test the robustness of input processors, they still struggle to produce or mutate complex inputs and interactions. LLM-based systems, on the other hand, can generate small example inputs, but fail to systematically explore the space of inputs and interactions as would be required for comprehensive testing. In this tutorial, we introduce test generation with fandango, a modern specification-based generator of test inputs and interactions. Based on a spec file that defines the structure and properties of the program input, fandango produces inputs that are syntactically and semantically correct, and systematically cover the input space of the program under test. In three interactive sessions, we (1) introduce language-based testing, (2) demonstrate how to use constraints to define desired properties, and then (3) delve into full-fledged protocol testing, producing entire interaction sequences between fandango and the network components under test. Participants are expected to bring a basic understanding of software testing; knowledge of python is a plus, but not required. At the end of the tutorial, they will (1) be able to specify and test formats for inputs and interactions, (2) produce comprehensive test suites using language-based techniques, and (3) understand the trade-offs and practical applications of language-based testing.