Rather than (basically) duplicating the `SimpleLinkService` in `test/driver.js`, with potential test failuires if you forget to update the test mock, it seems much nicer to just re-use the viewer component.
Note that `SimpleLinkService` is already bundled into the `build/components/pdf_viewer.js` file. Hence we only need to expose it similar to the other viewer components in that file, and make sure that the `gulp components` command runs as part of the test-setup.