AI systems, unlike traditional deterministic code, operate with non-determinism, continuous learning, and inherent biases, requiring a shift from execution checks to behavioral validation. This approach assesses AI agents' decision-making quality and appropriateness across diverse scenarios, focusing on five dimensions: memory, reflection, planning, action, and system reliability. Traditional QA methods fail AI systems because they rely on deterministic assumptions, missing the variability and context-dependency of AI outputs, and overlooking the cascade of errors that can propagate through decision chains. Behavioral validation emphasizes decision appropriateness over binary outcomes, evaluates multi-step reasoning processes, and checks if AI systems maintain safety, context relevance, and achieve user goals effectively. Core methodologies include end-to-end task flow validation, scenario-based testing, multi-agent interaction testing, and layered output evaluation, which are essential for identifying root cause errors and ensuring robust AI agent performance. Tools like Galileo enhance this validation by providing automated guardrails, real-time runtime protection, intelligent failure detection, and human-in-the-loop optimization, helping build reliable AI systems that align with user needs and business objectives.