Added ability to configure Jest via package.json (#1785)

- works when NOT ejected by merging default and app Jest options
- eject simply combines app and default into a single package.json jest field

Author: danjamin

packages/react-scripts/scripts/utils/createJestConfig.js

@@ -19,6 +19,8 @@ module.exports = (resolve, rootDir, isEjecting) => {
     ? '<rootDir>/src/setupTests.js'
     : undefined;
 
+  const appJestConfig = require(paths.appPackageJson).jest;
+
   // TODO: I don't know if it's safe or not to just use / as path separator
   // in Jest configs. We need help from somebody with Windows to determine this.
   const config = {
@@ -45,5 +47,10 @@ module.exports = (resolve, rootDir, isEjecting) => {
   if (rootDir) {
     config.rootDir = rootDir;
   }
-  return config;
+
+  if (Object.prototype.toString.call(appJestConfig) === '[object Object]') {
+    return Object.assign({}, config, appJestConfig);
+  } else {
+    return config;
+  }
 };

packages/react-scripts/template/README.md

@@ -46,6 +46,7 @@ You can find the most recent version of this guide [here](https://github.com/fac
 - [Pre-Rendering into Static HTML Files](#pre-rendering-into-static-html-files)
 - [Injecting Data from the Server into the Page](#injecting-data-from-the-server-into-the-page)
 - [Running Tests](#running-tests)
+  - [Configuring Jest](#configuring-jest)
   - [Filename Conventions](#filename-conventions)
   - [Command Line Interface](#command-line-interface)
   - [Version Control Integration](#version-control-integration)
@@ -924,6 +925,20 @@ While Jest provides browser globals such as `window` thanks to [jsdom](https://g
 
 We recommend that you use a separate tool for browser end-to-end tests if you need them. They are beyond the scope of Create React App.
 
+
+### Configuring Jest
+
+To override default configurations of Jest, simply add a `jest` field to your `package.json`, for example:
+
+```js
+"jest": {
+  "verbose": true,
+  "testResultsProcessor": "./node_modules/jest-junit"
+},
+```
+
+See [Jest Configuration](https://facebook.github.io/jest/docs/configuration.html) for more.
+
 ### Filename Conventions
 
 Jest will look for test files with any of the following popular naming conventions: