Atlas › 03 Agentic Testing Architectures › The ReAct Core Loop for Testing☰ Read as one page
The ReAct Core Loop for Testing
1.1From Scripts to Agents: A Fundamental ShiftTraditional test automation is imperative: you write step-by-step scripts that execute deterministically. Agentic testing is fundamentally…1.2The Four PhasesThe agent gathers information about the current state of the system under test. In browser testing, this means reading the page content…1.3A Complete ReAct Agent Implementation1.4Why ReAct Matters for TestingThe key insight: the agent does not follow a fixed script. It adapts its next action based on what it observes. This creates capabilities…1.5The History BufferThe history buffer is critical for preventing infinite loops and enabling learning within a test run.1.6Limitations of ReAct for Testing1. Non-deterministic. The same test objective may take different paths on different runs. This is a feature for exploration but a problem…1.7ReAct in Production Tools (as of July 2026)You rarely implement the raw loop yourself anymore. Production SDKs and frameworks package it, and you should be able to name them:1.8When to Use ReAct vs Scripts1.9Key TakeawayThe ReAct loop is the building block of all agentic testing. It transforms testing from "follow these exact steps" to "achieve this…