Added basic test coverage for the search index module

refs https://github.com/TryGhost/Team/issues/1665

- As with all the code we should be aiming for 100% test coverage :) This is a groundwork for testing code that uses HTTP requests
- nock was used as it's a library we use in the rest of the projects already

ghost/sodo-search/src/search-index.test.js

@@ -0,0 +1,19 @@
+import {init} from './search-index';
+import nock from 'nock';
+
+describe('search index', function () {
+    test('initializes search index', async () => {
+        const apiUrl = 'http://localhost/ghost/api/content';
+        const apiKey = 'secret_key';
+
+        const scope = nock('http://localhost/ghost/api/content')
+            .get('/posts/?key=secret_key&limit=all&fields=id,title,excerpt,url,updated_at,visibility&order=updated_at%20desc&formats=plaintext')
+            .reply(200, {
+                posts: [{}]
+            });
+
+        await init({apiUrl, apiKey});
+
+        expect(scope.isDone()).toBeTruthy();
+    });
+});