Run tests in parallel

What is needed to be able to run tests in parallel under the same host?

NOTE: all approaches are about test-executables running in parallel - not test-case parallelisation

This is because test-case (i.e. Qt test-function) level parallelisation is not supported by qtestlib.

Dumb parallelisation - via ctest -j N

This is almost impossible since tests have side-effects on the screen and on other system components like disk and network.

Isolating screen output for each executable

There are several alternative solutions:

• offscreen QPA plugin
• run each test under xvfb-run
  • slow since each test launches its own X server
• Start N number of virtual X servers (Xvfb or XVNC) or virtual wayland compositors (how?) and somehow rotate the DISPLAY setting on every test started.

Isolating system interference between test each executable

One way would be to run the tests under different users and inside different work directories. But is this really necessary? Do different tests read/write same locations?