How to use phpunit createMock etc inside codeception

Yii 2.0 Testing
1

Hi,
Need to run such mocks in codeception cest. But these methods are undefined in that context.

        $observer = $this->createMock(Observer::class);
        $observer->expects($this->once())
                 ->method('update')
                 ->with($this->equalTo('something'));

Also, Codeception has Stub which is not as flexible. Like I cannot use willReturnSelf() on mocked methods.

Stub::make('User', [
     'save' => \Codeception\Stub\Expected::once()
], $this);

My api.suite.yml

actor: ApiTester
modules:
    enabled:
      - Filesystem
      - Db
      - Yii2:
        part: [orm, email, fixtures]
      - Asserts
      - REST:
            url: http://localhost:8080/index-test.php/
            depends: Yii2
            part: JSON
            configFile: 'config/test.php'
        #- Helper\Api

Please suggest.
Thankls,
Vikas