switch to an alternate fs module to maintain testing strategy

Author: spalger

src/core/server/uuid/fs.ts

@@ -0,0 +1,24 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import Fs from 'fs';
+import { promisify } from 'util';
+
+export const readFile = promisify(Fs.readFile);
+export const writeFile = promisify(Fs.writeFile);

src/core/server/uuid/resolve_uuid.test.ts

@@ -17,28 +17,22 @@
  * under the License.
  */
 
-import Fs from 'fs';
 import { join } from 'path';
+import { readFile, writeFile } from './fs';
 import { resolveInstanceUuid } from './resolve_uuid';
 import { configServiceMock } from '../config/config_service.mock';
 import { loggingServiceMock } from '../logging/logging_service.mock';
 import { BehaviorSubject } from 'rxjs';
 import { Logger } from '../logging';
 
-const { readFile, writeFile } = Fs;
-
 jest.mock('uuid', () => ({
   v4: () => 'NEW_UUID',
 }));
 
-jest.mock('fs', () => {
-  const actual = jest.requireActual('fs');
-  return {
-    ...actual,
-    readFile: jest.fn().mockImplementation((...args) => process.nextTick(args.pop())),
-    writeFile: jest.fn().mockImplementation((...args) => process.nextTick(args.pop())),
-  };
-});
+jest.mock('./fs', () => ({
+  readFile: jest.fn(() => Promise.resolve('')),
+  writeFile: jest.fn(() => Promise.resolve('')),
+}));
 
 const DEFAULT_FILE_UUID = 'FILE_UUID';
 const DEFAULT_CONFIG_UUID = 'CONFIG_UUID';

src/core/server/uuid/resolve_uuid.ts

@@ -18,18 +18,14 @@
  */
 
 import uuid from 'uuid';
-import Fs from 'fs';
-import { promisify } from 'util';
 import { join } from 'path';
 import { take } from 'rxjs/operators';
+import { readFile, writeFile } from './fs';
 import { IConfigService } from '../config';
 import { PathConfigType, config as pathConfigDef } from '../path';
 import { HttpConfigType, config as httpConfigDef } from '../http';
 import { Logger } from '../logging';
 
-const readFile = promisify(Fs.readFile);
-const writeFile = promisify(Fs.writeFile);
-
 const FILE_ENCODING = 'utf8';
 const FILE_NAME = 'uuid';