How do I test an AI agent and know when it's reliable enough to trust?

You test agents with evals: a set of real tasks plus grading logic, run repeatedly because the same input can produce different outputs. Start embarrassingly simple: read 50 transcripts of your agent working, label every failure, turn the recurring ones into automated checks (code checks where possible, an LLM judge validated against your own labels where judgment is needed). Trust is earned per task: track pass rates over many runs, not one good demo.