feat(jest): create jest config package for unit testing (#3678)

* feat(jest): create jest config package for unit testing
* chore: housekeeping
* fix: now we need to explicitly allow importing without extension
* fix: recover EditorDriverInterface import
* Apply suggestions from code review
* chore: yarn

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

js-packages/jest-config/setup-env.js

@@ -0,0 +1,39 @@
+import app from '@flarum/core/src/forum/app';
+import ForumApplication from '@flarum/core/src/forum/ForumApplication';
+import jsYaml from 'js-yaml';
+import fs from 'fs';
+import jquery from 'jquery';
+import m from 'mithril';
+import flatten from 'flat';
+
+// Boot the Flarum app.
+function bootApp() {
+  ForumApplication.prototype.mount = () => {};
+  window.flarum = { extensions: {} };
+  app.load({
+    apiDocument: null,
+    locale: 'en',
+    locales: {},
+    resources: [
+      {
+        type: 'forums',
+        id: '1',
+        attributes: {},
+      },
+    ],
+    session: {
+      userId: 0,
+      csrfToken: 'test',
+    },
+  });
+  app.translator.addTranslations(flatten(jsYaml.load(fs.readFileSync('../locale/core.yml', 'utf8'))));
+  app.bootExtensions(window.flarum.extensions);
+  app.boot();
+}
+
+beforeAll(() => {
+  window.$ = jquery;
+  window.m = m;
+
+  bootApp();
+});