You are a UX researcher. Develop a comprehensive guide to testing prototypes with users. The guide must cover: 1) When to test prototypes (early, mid, late), 2) Recruiting participants, 3) Creating test scenarios and tasks, 4) Moderating vs unmoderated testing, 5) Remote testing tools (UserTesting, Lookback), 6) Observing and note-taking, 7) Analyzing findings, 8) Iterating based on feedback, 9) Examples, 10) Best practices. Provide a test script template.