[mocha] move setup work into module

with https://github.com/elastic/kibana/pull/5553 we added command line flags the told mocha it was supposed to use babel. This changes the strategy here and instead uses mocha's -r option (and it's mocha.opts file to specify it). This means that using mocha directly from the command line still works, and that we have a place where we can do other setup work.

package.json

@@ -55,8 +55,8 @@
     "elasticsearch": "grunt esvm:dev:keepalive",
     "lint": "grunt eslint:source",
     "lintroller": "grunt eslint:fixSource",
-    "mocha": "mocha --compilers js:babel/register",
-    "mocha:debug": "mocha --debug-brk --compilers js:babel/register"
+    "mocha": "mocha",
+    "mocha:debug": "mocha --debug-brk"
   },
   "repository": {
     "type": "git",

tasks/config/simplemocha.js

@@ -1,3 +1,11 @@
+var wrap = require('lodash').wrap;
+var Mocha = require('mocha');
+
+Mocha.prototype.run = wrap(Mocha.prototype.run, function (orig) {
+  require('../../test/mocha_setup');
+  orig.call(this);
+});
+
 module.exports = {
   options: {
     timeout: 10000,

test/mocha.opts

@@ -0,0 +1 @@
+-r test/mocha_setup.js

test/mocha_setup.js

@@ -0,0 +1 @@
+require('babel/register')(require('../src/optimize/babelOptions').node);