1.1From Scripts to Agents: A Fundamental Shift

Traditional test automation is imperative: you write step-by-step scripts that execute deterministically. Agentic testing is fundamentally different. An agent observes the state of the system, reasons about what to do next, acts, and evaluates the outcome -- all within a loop that can adapt to unexpected situations.

ReAct (Reason + Act) is the foundational pattern for agentic systems. Originally described for general-purpose LLM agents, it maps directly to testing workflows. As of July 2026, agentic testing is a mainstream discipline, not an experiment: the pattern you learn in this chapter is the engine inside production tools you will be asked about in interviews.