chore: support test for async function file loading

Author: AntiMoron

test/fixtures/loadfile/es-module-default-async.js

@@ -0,0 +1,13 @@
+"use strict";
+exports.__esModule = true;
+exports["default"] = {
+  fn() {
+    return new Promise((res) => {
+      setTimeout(() => {
+        res({
+          clients: 'Test Config'
+        });
+      }, 500);
+    });
+  },
+};

test/loader/load_file.test.ts

@@ -36,4 +36,10 @@ describe('test/loader/load_file.test.ts', () => {
     }
     assert.equal(result, '---\nmap:\n a: 1\n b: 2');
   });
+
+  it('should load file which returns async function', async () => {
+    app = createApp('load_file');
+    const result = (await app.loader.loadFile(getFilepath('load_file/es-module-default-async.yml'))).toString();
+    assert.deepEqual(result, { clients: 'Test Config' });
+  });
 });