New test helper for getting the underlying CodeMirror instance from a dom selector

ui/tests/.eslintrc.js

@@ -5,6 +5,7 @@ module.exports = {
     selectSearch: true,
     removeMultipleOption: true,
     clearSelected: true,
+    getCodeMirrorInstance: true,
   },
   env: {
     embertest: true,

ui/tests/helpers/codemirror.js

@@ -0,0 +1,19 @@
+import { registerHelper } from '@ember/test';
+
+const invariant = (truthy, error) => {
+  if (!truthy) throw new Error(error);
+};
+
+export default function registerCodeMirrorHelpers() {
+  registerHelper('getCodeMirrorInstance', function(app, selector) {
+    const cmService = app.__container__.lookup('service:code-mirror');
+
+    const element = document.querySelector(selector);
+    invariant(element, `Selector ${selector} matched no elements`);
+
+    const cm = cmService.instanceFor(element.id);
+    invariant(cm, `No registered CodeMirror instance for ${selector}`);
+
+    return cm;
+  });
+}

ui/tests/helpers/start-app.js

@@ -3,8 +3,10 @@ import { merge } from '@ember/polyfills';
 import Application from '../../app';
 import config from '../../config/environment';
 import registerPowerSelectHelpers from 'ember-power-select/test-support/helpers';
+import registerCodeMirrorHelpers from 'nomad-ui/tests/helpers/codemirror';
 
 registerPowerSelectHelpers();
+registerCodeMirrorHelpers();
 
 export default function startApp(attrs) {
   let attributes = merge({}, config.APP);