Improve code coverage for coverage merging

[yannbf]

This PR:

• Updates the coverage functionality to generate a coverage/storybook/coverage-storybook.json file after running with --coverage
• Uses @storybook/addon-coverage internally
• Updates README for better instructions, including usage of @storybook/addon-coverage
• Separates testing workflows and sets up Codecov

If people use tools like Codecov and generate multiple coverage reports (e.g. Jest + Storybook), Codecov will detect them automatically and merge them. For people who want to make a full coverage map locally, they will have to do a bit of scripting:

• Move coverage/storybook/coverage-storybook.json to coverage/coverage-storybook.json
• Run npx nyc report --reporter=lcov -t coverage --report-dir coverage

📦 Published PR as canary version: 0.2.1--canary.130.4d54d5b.0

✨ Test out this PR locally via:

npm install @storybook/test-runner@0.2.1--canary.130.4d54d5b.0
# or 
yarn add @storybook/test-runner@0.2.1--canary.130.4d54d5b.0

Version

Published prerelease version: v0.3.0-next.1

Changelog

Release Notes

Support code coverage (#120)

Support code coverage (#120)

---

🚀 Enhancement

• Support code coverage #120 (@yannbf)

🐛 Bug Fix

• Improve code coverage for coverage merging #130 (@yannbf)

Authors: 1

• Yann Braga (@yannbf)

[shilman]

This looks good to me. So, to confirm, json reports can be merged across directories? From our earlier conversation I was under the impression that the two json files needed to be in the same directory.

[yannbf]

This looks good to me. So, to confirm, json reports can be merged across directories? From our earlier conversation I was under the impression that the two json files needed to be in the same directory.

They are extracted automatically by tools like Codecov. Tools like nyc do not merge across directories. I added a recipe for that