If an error message pops up after clicking on "Execute Test" stating:
An error occurred while running a test.
Object reference not set to an instance of an object.
It is cause by a well known problem of Coala. A§E Coala does not support DPI resolution higher than 100%. This problem has been fixed with the updated version.
To solve this issue follow this guide to reduce your screen DPI and restart Coala.
If the problem persist don't hesitate to contact us.