Write new Slack HTTP integration tests in tests/ using the shared MSW harness and Slack fixtures.

Step 1: Classify the test

Use this skill only when the test validates outbound Slack HTTP behavior, including:

Slack Web API method calls from src/chat/slack-actions/*
Slack file upload HTTP flow (files.getUploadURLExternal + files.slack.com/upload/* + files.completeUploadExternal)
Slack user lookup fetches in src/chat/slack-user.ts

If the target test is pure business logic with no Slack HTTP contract assertions, use a normal unit test and skip this skill.

Step 2: Load only required references

Need	Read
End-to-end authoring workflow	`${CLAUDE_SKILL_ROOT}/references/test-authoring-playbook.md`
Endpoint and fixture mapping	`${CLAUDE_SKILL_ROOT}/references/endpoint-fixture-matrix.md`
Existing bad patterns to avoid	`${CLAUDE_SKILL_ROOT}/references/anti-patterns-and-fixes.md`