Framework for dealing with fast and slow test runs

[Martin Sandve Alnæs]

A general approach to dealing with slow tests: Marking slow tests with pytest and make cmake-targets running only fast tests. We could even have three levels: fast, normal, and slow. The slow can be run nightly, the normal on the buildbot, and the fast during local development.

This needs buy-in from all the devs and continuous small improvements over time to stay useful. Please provide opinions. @logg @garth-wells @blechta @chris_richardson

I also wish to remind you that you can run subsets of tests while working.

[Marie Elisabeth Rognes]

I've been using this (slow/medium/fast) for cbcbeat for some time and finds that it works well.

[Anders Logg (Chalmers)]

Yes this sounds great. This will also have the side-effect that slow tests will be marked and we may consider whether they actually need to be that slow and possibly speed those tests up.

[Prof Garth Wells]

I don't see the point of fast and slow tests. One wants to run all tests before pushing to next/master, which means running fast and slow tests. Distinguishing between the two doesn't buy anything.

[Anders Logg (Chalmers)]

Removing milestone: 1.8 (automated comment)