Improve test suite with deterministic test #12
Description
The very first test in the test suite fails. Locally on my computer it runs fine, but online it doesn't work.
Regardless, we have to improve this test. Now I am using a 1D energy balance model that is bistable. That is not a good approach. We should instead construct a stable linear 2D system, and add a 3rd equation of an exponential relaxation that relaxes to a function of the first two variables. There we know analytically what the fixed point solution should be! We should check that this system gives the correct ODEProblem then!