Add the possibility to enforce a fixed laplacian + equation factory tests #644
Description
Is your feature request related to a problem? Please describe.
The equation_factory.py file provides classes to impose a constant value for all operators implemented in PINA. For instance, one can impose a fixed gradient or divergence using FixedGradient and FixedFlux, respectively. Similarly, a fixed value on the output can be imposed using FixedValue.
However, this cannot be done for the laplacian, as the class Laplace allows to impose only null laplacians.
Moreover, classes in the equation_factory.py file are currently not tested.
Describe the solution you'd like
The Laplace class should work in a similar fashion as FixedGradient or FixedFlux, and its name should be updated to FixedLaplacian.
Unit tests for the equation_factory.py file should be added.