[FEATURE] fsInterface: Add mkdir function

When working with the UI5 adapters, it is not necessary to create
directories. Therefore it's basically a noop

lib/fsInterface.js

@@ -1,10 +1,15 @@
 /**
- * Wraps readers to access them like a node fs-interface.
+ * Wraps readers to access them through a [Node.js fs]{@link https://nodejs.org/api/fs.html} styled interface.
  *
  * @public
  * @alias module:@ui5/fs.fsInterface
  * @param {module:@ui5/fs.AbstractReader} reader Resource Reader or Collection
- * @returns {Object} Object with fs-style functions <code>readFile</code>, <code>stat</code> and <code>readdir</code>
+ *
+ * @returns {Object} Object with [Node.js fs]{@link https://nodejs.org/api/fs.html} styled functions
+ * [<code>readFile</code>]{@link https://nodejs.org/api/fs.html#fs_fs_readfile_path_options_callback},
+ * [<code>stat</code>]{@link https://nodejs.org/api/fs.html#fs_fs_stat_path_options_callback},
+ * [<code>readdir</code>]{@link https://nodejs.org/api/fs.html#fs_fs_readdir_path_options_callback} and
+ * [<code>mkdir</code>]{@link https://nodejs.org/api/fs.html#fs_fs_mkdir_path_options_callback}
  */
 module.exports = (reader) => {
 	return {
@@ -65,6 +70,9 @@ module.exports = (reader) => {
 				});
 				callback(null, files);
 			}).catch(callback);
+		},
+		mkdir(path, callback) {
+			setTimeout(callback, 0);
 		}
 	};
 };

test/lib/fsInterface.js

@@ -100,3 +100,13 @@ test("fs: stat", (t) => {
 	const stat = promisify(fs.stat);
 	return assertStat(t, stat, path.join(__dirname, "..", "fixtures", "fsInterface"), "/foo.txt");
 });
+
+test("MemAdapter: mkdir", async (t) => {
+	const memAdapter = new MemAdapter({
+		virBasePath: "/"
+	});
+	const fs = fsInterface(memAdapter);
+	const mkdir = promisify(fs.mkdir);
+
+	await t.notThrows(mkdir("pony"), "mkdir executes successfully");
+});