CI for OS X and Windows

[tpapp]

Possibly the following pattern, which is already in use for CI on Linux (Travis), could work:

• create a file with some type/extension, associated with program
• check that program is not (accidentally) running (so that tests are meaningful)
• DefaultApplication.open() the file,
• check that program is now running.

TODO:

• tests for OS X
• tests for Windows (use Appveyor or similar?)