Adapt findInstalled for unit tests

packages/gitbook/src/plugins/__tests__/findInstalled.js

@@ -17,7 +17,7 @@ describe('findInstalled', function() {
         .then(function(plugins) {
             expect(plugins.size >= gitbookPlugins.size).toBeTruthy();
 
-            expect(plugins.has('fontsettings')).toBe(true);
+            expect(plugins.has('highlight')).toBe(true);
             expect(plugins.has('search')).toBe(true);
         });
     });

packages/gitbook/src/plugins/findInstalled.js

@@ -41,9 +41,14 @@ function readModule(modulePath, depth, parent) {
  * @param {String} folder
  * @param {Number} depth
  * @param {String} parent
- * @return {OrderedMap<String:Plugin>}
+ * @return {Promise<OrderedMap<String:Plugin>>} plugins
  */
 function findInstalled(folder, depth = 0, parent = null) {
+    // When tetsing with mock-fs
+    if (!folder) {
+        return Promise(OrderedMap());
+    }
+
     // Search for gitbook-plugins in node_modules folder
     const node_modules = path.join(folder, 'node_modules');
 

packages/gitbook/src/plugins/loadPlugin.js

@@ -15,13 +15,13 @@ function isModuleNotFound(err) {
 }
 
 /**
-    Load a plugin in a book
-
-    @param {Book} book
-    @param {Plugin} plugin
-    @param {String} pkgPath (optional)
-    @return {Promise<Plugin>}
-*/
+ * Load a plugin in a book
+ *
+ * @param {Book} book
+ * @param {Plugin} plugin
+ * @param {String} pkgPath (optional)
+ * @return {Promise<Plugin>}
+ */
 function loadPlugin(book, plugin) {
     const logger = book.getLogger();