Add better dev/test instructions in CONTRIBUTING.md

[jack-lewin]

Hi,

I'm hoping to contribute to enzyme, but I'm having trouble running the test suite. Not sure if I've missed anything with the setup, but I'd appreciate some help getting up and running! Thanks a lot.

Steps taken:

1. git clone https://github.com/airbnb/enzyme
2. cd enzyme
3. npm install
4. npm run react:15 - this waits for ~10 secs, and then exits without feedback. Not sure whether that's the issue?
5. npm test fails, with a linter error.

Error message:

/path/to/enzyme/packages/enzyme-adapter-react-15/src/ReactFifteenAdapter.js

lerna ERR! execute   10:31  error  Unable to resolve path to module 'enzyme'                import/no-unresolved
lerna ERR! execute   10:31  error  Missing file extension for "enzyme"                      import/extensions
lerna ERR! execute   20:8   error  Unable to resolve path to module 'enzyme-adapter-utils'  import/no-unresolved
lerna ERR! execute   20:8   error  Missing file extension for "enzyme-adapter-utils"        import/extensions

List of globally-installed packages:

├── create-react-app@1.4.1
├── eslint@4.7.2
├── eslint-plugin-import@2.7.0
├── jest@21.2.0
├── lerna@2.2.0
├── npm@5.4.2
├── serve@6.1.0
├── standard@10.0.3
└── yarn@1.1.0

[lelandrichardson]

Hey @jack-lewin, you're right - we should add some steps to the contributing guide.

Due to our repo structure and hard to explain things, our test suite currently runs on built enzyme. This means you need to run npm run build before running the test suite.

If you are actively developing, the workflow I recommend is to run npm run build:watch in one terminal, and npm run test:watch in another terminal. This should provide you with ~realtime feedback.

[jack-lewin]

@lelandrichardson thanks for clearing that up - I've got it built & running now. I'll put in a PR for the docs over the weekend!

[ljharb]

Merged in #1207.