Hello Speak Example - Mock engine does not work

Description:

The "mock" engine does not work, no sound is produced when using it.

Steps to reproduce:

Open the Hello speak example.

Change the engine from "default" to "mock"

Click on "Speak"

Expected behavior:

The engine should work properly and provide an audio when clicking on speak.
Observed behavior:

The "mock" engine doesn't seem to work and no audio is heard when clicking on speak. 
Special notes:

The default "sapi" engine works without any issue.