feat(jest-environment-puppeteer): accept a promise as config (#178)

packages/jest-environment-puppeteer/README.md

@@ -79,7 +79,7 @@ it('should put test in debug mode', async () => {
 
 ### `jest-puppeteer.config.js`
 
-You can specify a `jest-puppeteer.config.js` at the root of the project or define a custom path using `JEST_PUPPETEER_CONFIG` environment variable.
+You can specify a `jest-puppeteer.config.js` at the root of the project or define a custom path using `JEST_PUPPETEER_CONFIG` environment variable. It should export a config object or a Promise for a config object.
 
 - `launch` <[object]> [All Puppeteer launch options](https://github.com/GoogleChrome/puppeteer/blob/master/docs/api.md#puppeteerlaunchoptions) can be specified in config. Since it is JavaScript, you can use all stuff you need, including environment.
 - `connect` <[object]> [All Puppeteer connect options](https://github.com/GoogleChrome/puppeteer/blob/master/docs/api.md#puppeteerconnectoptions) can be specified in config. This is an alternative to `launch` config, allowing you to connect to an already running instance of Chrome.
@@ -113,19 +113,26 @@ This example uses an already running instance of Chrome by passing the active we
 
 ```js
 // jest-puppeteer.config.js
-const wsEndpoint = fs.readFileSync(endpointPath, 'utf8')
-
-module.exports = {
-  connect: {
-    browserWSEndpoint: wsEndpoint,
-  },
-  server: {
-    command: 'node server.js',
-    port: 4444,
-    launchTimeout: 10000,
-    debug: true,
-  },
+const fetch = require('node-fetch')
+const dockerHost = 'http://localhost:9222'
+
+async function getConfig () {
+  const response = await fetch(`${dockerHost}/json/version`)
+  const browserWSEndpoint = (await response.json()).webSocketDebuggerUrl
+  return {
+    connect: {
+      browserWSEndpoint
+    },
+    server: {
+      command: 'node server.js',
+      port: 3000,
+      launchTimeout: 10000,
+      debug: true,
+    }
+  }
 }
+
+module.exports = getConfig()
 ```
 
 ## Inspiration

packages/jest-environment-puppeteer/src/readConfig.js

@@ -44,7 +44,7 @@ async function readConfig() {
   }
 
   // eslint-disable-next-line global-require, import/no-dynamic-require
-  const localConfig = require(absConfigPath)
+  const localConfig = await require(absConfigPath)
   return merge({}, defaultConfig, localConfig)
 }
 

packages/jest-environment-puppeteer/tests/__fixtures__/promiseConfig.js

@@ -0,0 +1,5 @@
+module.exports = Promise.resolve({
+  server: {
+    command: 'yarn babel-node src/server/main.js',
+  },
+})

packages/jest-environment-puppeteer/tests/readConfig.test.js

@@ -68,4 +68,16 @@ describe('readConfig', () => {
       ])
     })
   })
+
+  describe('with Promise returning config', () => {
+    it('should return async config', async () => {
+      process.env.JEST_PUPPETEER_CONFIG = path.resolve(
+        __dirname,
+        '__fixtures__/promiseConfig.js',
+      )
+      mockExists(true)
+      const config = await readConfig()
+      expect(config.server).toBeDefined()
+    })
+  })
 })