__PATH_PREFIX__ for testing with enzyme/jest

[daniellizik]

Related to #1378

I'm still seeing this in a enzyme/jest test:

gatsby-config.js

module.exports = {
  // this doesn't affect the test at all, it seems
  pathPrefix: ' '
};

test

import { render } from 'enzyme';
import { Link } from 'gatsby';

it('renders', () => {
  const wrapper = render(<Link to="/foo" />);
  // ReferenceError: __PATH_PREFIX__ is not defined
});

// this one is fine
it('provides the expected global', () => {
  global.__PATH_PREFIX__ = 'test';
  const wrapper = render(<Link to="/foo" />);
});

The docs on pathPrefix don't explicitly mention what to do during testing

During development, write paths as if there was no path prefix e.g. for a blog hosted at example.com/blog, don’t add /blog to your links. The prefix will be added when you build for deployment.

Maybe here it would be better to do something like

export function withPrefix(path) {
  const pathPrefix = typeof __PATH_PREFIX__ !== 'undefined' ? __PATH_PREFIX__ : '';
  return normalizePath(`${pathPrefix}/${path}`)
}

Probably a better solution would be to inject the global if NODE_ENV is test?

[gatsbot]

	Fails
🚫	Danger failed to run /app/danger-0.mxj5fujn0ls.ts,/app/danger-0.1ueluu1v0to.ts.

Error Error

ENOENT: no such file or directory, open '/app/danger-0.1ueluu1v0to.ts'

Error: ENOENT: no such file or directory, open '/app/danger-0.1ueluu1v0to.ts'
    at Object.openSync (fs.js:439:3)
    at Object.readFileSync (fs.js:344:35)
    at Object.<anonymous> (/app/node_modules/danger/distribution/runner/runners/vm2.js:106:87)
    at step (/app/node_modules/danger/distribution/runner/runners/vm2.js:43:23)
    at Object.next (/app/node_modules/danger/distribution/runner/runners/vm2.js:24:53)
    at fulfilled (/app/node_modules/danger/distribution/runner/runners/vm2.js:15:58)
    at process._tickCallback (internal/process/next_tick.js:68:7)

Dangerfile

import { danger, markdown } from "danger"

const getMessage = (username: string) => `\
@${username} We noticed that the body of this issue is blank.

Please fill in this field with more information to help the \
maintainers resolve your issue.\
`

export const emptybody = () => {
  const {
    user: { login: username },
    body,
  } = danger.github.issue as any

  if (body.trim().length === 0) {
    markdown(getMessage(username))
  }
}

export default async () => {
  emptybody()
}

---

Generated by 🚫 dangerJS

[daniellizik]

sorry found this https://www.gatsbyjs.org/docs/unit-testing/#2-creating-a-configuration-file-for-jest