Enhance cmesh testing

[Davknapp]

This is a draft PR to discuss further needed changes of this new feature.

This branch provides a way to iterate over all of our cmeshes using googletest functionality.
It basically consists of two classes.

• The base class cmesh_creator, a class to create cmeshes of similar type (for example all cmeshes that only need a communicator). It also holds the cmesh.
• The class cmesh_generator, iterates over all cmesh_creators and all of the parameter-sets usable by each cmesh_creator. Overloads the +and < to be usable by testing::Range(start, end, step)` of the GoogleTestSuite.

I implemented two examples of a cmesh_creator, one for cmesh-examples that only get a communicator and one for examples that get a communicator and a number of trees.

Goal of this feature is to provide a way to test cmeshes, that is easily extendable by new testcases.
In the current setup one would either:
a) Add the new cmesh function to one of the existing cmesh_creators or
b) Implement a new 'cmesh_creator' and add it to the 'cmesh_generator'

As soon as this PR is merged, we would also be able to provide a MAKRO to iterate over all cmeshes and a customized assertion to check the equality of two cmeshes.

I will be happy about your opinion on this new feature!

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As a reviewer please read through all the code lines and make sure that the code is fully understood, bug free, well-documented and well-structured.

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Tests

• The code is covered in an existing or new test case using Google Test

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Licence

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[jmark]

Thanks for the interesting contribution @Davknapp !

I like the idea very much and we should definitely consider to migrate to this testing scheme soon!

However, in my view creating three C++ classes for this rather simple logic is shooting birds with guns. I suggest to consider a refactor.

As also noted in the line attached comments I suggest to simply create one C++ iterator class which spits out one cmesh after the other. Very simple, easy to comprehend and quick to extend with lots of cmesh variants.

Here some links. Probably just implement an output iterator. One proably does not need to implement all operators. We do not need to apply sort or random access or such fancy stuff.

https://www.internalpointers.com/post/writing-custom-iterators-modern-cpp
https://www.programiz.com/cpp-programming/iterators

[Davknapp]

Thanks for the interesting contribution @Davknapp !

I like the idea very much and we should definitely consider to migrate to this testing scheme soon!

However, in my view creating three C++ classes for this rather simple logic is shooting birds with guns. I suggest to consider a refactor.

As also noted in the line attached comments I suggest to simply create one C++ iterator class which spits out one cmesh after the other. Very simple, easy to comprehend and quick to extend with lots of cmesh variants.

Here some links. Probably just implement an output iterator. One proably does not need to implement all operators. We do not need to apply sort or random access or such fancy stuff.

https://www.internalpointers.com/post/writing-custom-iterators-modern-cpp https://www.programiz.com/cpp-programming/iterators

The goal is to be able to run tests over a sum of cmeshes. I agree, for a single set of cmeshes (for example all cmeshes that only need a communicator, or all cmeshes that get a communicator and a number of trees to generate) it will be better to implement an iterator.
We want to iterate over varying number of parameters (not all functions creating a cmesh have the same number of arguments), this we way, we are able to specify how we iterate over a subset. Furthermore not all functions create valid cmeshes for all parameters, this way we are able to prevent such cmeshes. Additionally we can use the step to skip entire subsets of cmeshes. Maybe it is a good idea to have a call about this subject ;)

[jmark]

Let's have a direct telco about this PR. It is pretty tedious to get an overview over the interdependence of classes you use here and how and where they are used.