The Coding Stage
Developers need to closely follow the guidelines set up in the design stage. Say it's been decided that the introductory window will have a scrolling banner at the top; the banner runs with an audio clip that reads the banner the first time across. But it's also been decided that certain restrictions should apply. If a screen reader is detected, the banner will appear once and not scroll. An option that the user can set will be available to turn off the audio clip. Developers need to find the system and programming tools to implement these design guidelines. There might be cases where the user will find the workaround to be too difficult to bother with. Since this is an introductory screen, the sound clip begins playing at the same time the user has access to the disabling mechanism. By the time the user can disable the clip, it's already played. So the developers determine this design guideline to be impractical. However, they are free to come up with an alternative. The developers decide to include a button on the introductory screen that will play the audio clip when the button is pressed.
The Testing Stage
Part of the guidelines for testers in any organization should be testing accessibility features. Every test plan should have guidelines outlining testing with the different system accessibility options set. Screen resolutions should be specified and tests without the mouse should be planned. Most important, find testers with disabilities. If you don't have anyone on staff, organizations exist throughout most of the software-developing world where you can find the testers you need.