feat(unit-jest): run jest in the same process

This allows vue-cli-service test:unit to be debugged via node inspector.

packages/@vue/cli-plugin-unit-jest/README.md

@@ -15,6 +15,16 @@
 
   All [Jest command line options](https://facebook.github.io/jest/docs/en/cli.html) are also supported.
 
+## Debugging Tests
+
+Note that directly running `jest` will fail because the Babel preset requires hints to make your code work in Node.js, so you must run your tests with `vue-cli-service test:unit`.
+
+If you want to debug your tests via the Node inspector, you can run the following:
+
+``` sh
+node --inspect-brk ./node_modules/.bin/vue-cli-service test:unit
+```
+
 ## Configuration
 
 Jest can be configured via `jest.config.js` in your project root, or the `jest` field in `package.json`.

packages/@vue/cli-plugin-unit-jest/index.js

@@ -12,24 +12,7 @@ module.exports = api => {
     // for @vue/babel-preset-app
     process.env.VUE_CLI_BABEL_TARGET_NODE = true
     process.env.VUE_CLI_BABEL_TRANSPILE_MODULES = true
-
-    const { execa } = require('@vue/cli-shared-utils')
-    const jestBinPath = require.resolve('jest/bin/jest')
-
-    return new Promise((resolve, reject) => {
-      const child = execa(jestBinPath, rawArgv, {
-        cwd: api.resolve('.'),
-        stdio: 'inherit'
-      })
-      child.on('error', reject)
-      child.on('exit', code => {
-        if (code !== 0) {
-          reject(`jest exited with code ${code}.`)
-        } else {
-          resolve()
-        }
-      })
-    })
+    require('jest').run(rawArgv)
   })
 
   // TODO remove in RC