Document how to structure/write new integration tests

[tyll]

Topics:

• [ ] How many tests per file
• [ ] How to use the helpers
• [ ] How to name/tag tests to simplify test selection
• [ ] How to use blocks, check for failures
• [ ] What to test
• [ ] Speeding things up by testing the module directly
• [ ] Using test IP addresses like https://tools.ietf.org/html/rfc5737
• [ ] tagging cleanup
• [ ] ...