LLMCFG-TGen: Using LLM-Generated Control Flow Graphs to Automatically Create Test Cases from Use Cases

Abstract

Appropriate test-case generation is critical in software testing and significantly impacts testing quality. Requirements-Based Test Generation (RBTG) derives test cases from software requirements to verify whether system behavior aligns with user needs and expectations. Requirements are often documented in Natural Language (NL), with use-case descriptions being a popular method for capturing functional behaviors and interaction flows in a structured, readable form. Recently, Large Language Models (LLMs) have shown strong potential for automating test generation from NL requirements. However, existing LLM-based approaches often fail to ensure comprehensive and non-redundant coverage, and may not adequately capture complex conditional logic, leading to incomplete test cases. To address these limitations, we propose an end-to-end approach called Test Generation based on LLM-generated Control Flow Graphs (LLMCFG-TGen), which generates test cases from NL use-case descriptions. It consists of three steps: (1) CFG Generation, where an LLM transforms a use case into a structured JSON-based Control Flow Graph capturing all potential branches; (2) Test-Path Extraction, where the CFG is traversed to derive execution paths; and (3) Test-Case Creation, where test cases are generated from these paths. We evaluate the approach on six use-case datasets across diverse domains. Results show that LLMs can effectively construct structured CFGs from NL use cases. Compared with two baselines, LLMCFG-TGen produces more complete and structurally consistent test cases by better capturing behavioral logic and execution flows. Both LLM-based and practitioner-based evaluations further confirm improved comprehensiveness and logical coherence while reducing manual effort.