Draft: CollectionsUnitTests for LinearAdvectionDiffusionReaction operator

Issue/feature addressed

There is no unit test for the LinearADR operator in Collections.

Proposed solution

Add unit tests similar to the tests in library/UnitTests/Collections/Test*.

Implementation

Adapted the unit tests based on the Helmholtz operator tests, but added varcoeffs.

Tests

• Unit tests for each element type (except 1D/Segments)

Suggested reviewers

@CFD-Xing

Notes

• There is a lot of copy and waste code in the CollectionUnitTests.

Checklist

• Functions and classes, or changes to them, are documented.
• [ ] User guide/documentation is updated.
• Changelog is updated.
• Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• [ ] License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).