fix(MongoMemoryServer::getStartOptions): use "forceSamePort", even wh…

…en instance is not defined

fixes #578

packages/mongodb-memory-server-core/src/MongoMemoryServer.ts

@@ -326,17 +326,27 @@ export class MongoMemoryServer extends EventEmitter implements ManagerAdvanced {
   /**
    * Construct Instance Starting Options
    */
-  protected async getStartOptions(): Promise<MongoMemoryServerGetStartOptions> {
-    this.debug('getStartOptions');
+  protected async getStartOptions(
+    forceSamePort: boolean = false
+  ): Promise<MongoMemoryServerGetStartOptions> {
+    this.debug(`getStartOptions: forceSamePort: ${forceSamePort}`);
     /** Shortcut to this.opts.instance */
     const instOpts = this.opts.instance ?? {};
     /**
      * This variable is used for determining if "createAuth" should be run
      */
     let isNew: boolean = true;
 
+    // use pre-defined port if available, otherwise generate a new port
+    let port = typeof instOpts.port === 'number' ? instOpts.port : undefined;
+
+    // if "forceSamePort" is not true, and get a available port
+    if (!forceSamePort || isNullOrUndefined(port)) {
+      port = await this.getNewPort(port);
+    }
+
     const data: StartupInstanceData = {
-      port: await this.getNewPort(instOpts.port),
+      port: port,
       dbName: generateDbName(instOpts.dbName),
       ip: instOpts.ip ?? '127.0.0.1',
       storageEngine: instOpts.storageEngine ?? 'ephemeralForTest',
@@ -412,7 +422,7 @@ export class MongoMemoryServer extends EventEmitter implements ManagerAdvanced {
       return;
     }
 
-    const { mongodOptions, createAuth, data } = await this.getStartOptions();
+    const { mongodOptions, createAuth, data } = await this.getStartOptions(forceSamePort);
     this.debug(`_startUpInstance: Creating new MongoDB instance with options:`, mongodOptions);
 
     const instance = await MongoInstance.create(mongodOptions);
@@ -473,6 +483,7 @@ export class MongoMemoryServer extends EventEmitter implements ManagerAdvanced {
     }
 
     // assert here, otherwise typescript is not happy
+    // TODO: remove check, typescript does not need this anymore
     assertion(
       !isNullOrUndefined(this._instanceInfo.instance),
       new Error('"instanceInfo.instance" is undefined!')

packages/mongodb-memory-server-core/src/__tests__/MongoMemoryServer.test.ts

@@ -679,6 +679,54 @@ describe('MongoMemoryServer', () => {
       expect(readdirSpy).toHaveBeenCalledTimes(1);
       expect(options.createAuth).toEqual(false);
     });
+
+    it('should generate a port when no suggestion is defined', async () => {
+      const mongoServer = new MongoMemoryServer();
+      const newPortSpy = jest
+        // @ts-expect-error "getNewPort" is protected
+        .spyOn(mongoServer, 'getNewPort')
+        // @ts-expect-error it somehow gets a wrong function type
+        .mockImplementation((port) => Promise.resolve(port ? port : 2000));
+
+      // @ts-expect-error "getStartOptions" is protected
+      const options = await mongoServer.getStartOptions();
+
+      expect(newPortSpy).toHaveBeenCalledTimes(1);
+      expect(typeof options.data.port === 'number').toBeTruthy();
+    });
+
+    it('should use a predefined port as a suggestion for a port', async () => {
+      const predefinedPort = 10000;
+
+      const mongoServer = new MongoMemoryServer({ instance: { port: predefinedPort } });
+      const newPortSpy = jest
+        // @ts-expect-error "getNewPort" is protected
+        .spyOn(mongoServer, 'getNewPort')
+        // @ts-expect-error it somehow gets a wrong function type
+        .mockImplementation((port) => Promise.resolve(port ? port : 2000));
+
+      // @ts-expect-error "getStartOptions" is protected
+      const options = await mongoServer.getStartOptions();
+
+      expect(newPortSpy).toHaveBeenCalledWith(predefinedPort);
+      expect(options.data.port).toStrictEqual(predefinedPort);
+    });
+
+    it('should use a predefined port for a port with "forceSamePort" on', async () => {
+      const predefinedPort = 30000;
+
+      const mongoServer = new MongoMemoryServer({ instance: { port: predefinedPort } });
+      const newPortSpy = jest
+        // @ts-expect-error "getNewPort" is protected
+        .spyOn(mongoServer, 'getNewPort')
+        .mockImplementation(() => fail('Expected this function to not be called'));
+
+      // @ts-expect-error "getStartOptions" is protected
+      const options = await mongoServer.getStartOptions(true);
+
+      expect(newPortSpy).not.toHaveBeenCalled();
+      expect(options.data.port).toStrictEqual(predefinedPort);
+    });
   });
 
   it('"getDbPath" should return the dbPath', async () => {