[ci] refactor: add tests Guide

[moran365]

Summary

Changes

• add test case guidebook

PR title

Use [area] type: summary.

• Areas: agents, framework, gateway, logging, sandbox, tasks, tools, training, app, docs, examples, ci, build, deps, misc
• Types: feat, fix, refactor, perf, test, docs, chore, revert
• Separate multiple areas with comma-space: [agents, sandbox] feat: add isolated harness execution
• Prefix compatibility-breaking work with [BREAKING]: [BREAKING][tasks, docs] refactor: replace task config schema
• A stacked series may start with [1/N]: [1/N][gateway] refactor: split protocol adapters

Checklist

• The PR is focused and linked to an issue or explains why no issue is needed.
• The title follows the format above and names the layer that owns the change.
• Tests cover the behavior, or the Validation section explains why they are not practical.
• User-facing API, config, and workflow changes include documentation or runnable examples.
• Compatibility impact and migration steps are documented.
• Logs, fixtures, and examples contain no credentials or private data.
• pre-commit run --all-files --show-diff-on-failure passes.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.

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