MMS testing

[jhdark]

Proposed changes

MMS testing! This PR starts to build up an MMS testing suite for vigorous verification testing. @RemDelaporteMathurin See what you think so far. I've adapted the tests in fenicsx tutorial.

Types of changes

What types of changes does your code introduce to FESTIM?

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Code refactoring
• Documentation Update (if none of the other choices apply)
• New tests

Checklist

• Black formatted
• Unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.24%. Comparing base (be788e4) to head (5a9bd96).
Report is 11 commits behind head on fenicsx.

Additional details and impacted files

@@             Coverage Diff             @@
##           fenicsx     #663      +/-   ##
===========================================
+ Coverage    99.05%   99.24%   +0.18%     
===========================================
  Files           26       26              
  Lines         1168     1186      +18     
===========================================
+ Hits          1157     1177      +20     
+ Misses          11        9       -2     

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[RemDelaporteMathurin]

This looks very good.

We need to define a test matrix like varying temperature, transient, flux boundary condition, 2D, etc. to make sure we cover all the features of the code.

Also I would add some general documentation (comments) to explain what's done in the test.

[jhdark]

@RemDelaporteMathurin here are basic examples of the types of MMS tests we could do. But perhaps we can discuss further in the general channel on Slack for what should be covered with MMS testing

[jhdark]

I rebased from fenicsx, but theres still, if not more, changes that are already in that branch? Not sure if I should merge or not?

[jhdark]

Remaking PR due to bugs from not detecting changes to fenicsx branch