Add tests for the presenter of elwin interface

[adriazalvarez]

Description of work

This PR follows after refactoring the presenter of the elwin interface and making it non qt-dependent (#36537). Now test are added for most public members of the class.
To make it possible to test by mocking the models and the data model, I had to add a new overloaded constructor to the elwin presenter which is only called from the test. All Data Manipulation presenter classes share the same structure, so maybe we can think of adding an issue in the future for homogenizing the presenters and constructing them by passing directly unique pointers to the model, as it is done on most other presenter of mantid MVP interfaces.

Summary of work

Fixes #34928

Further detail of work

To test:

• Test passes in CI
• Code review

** does not need release notes**

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[robertapplin]

I've only had a very quick look, and it looks great! The only think I would say is that it would be better for the MockElwinModel to inherit from an interface class rather than the ElwinModel. Was there a reason you did it this way?

[adriazalvarez]

Thanks for taking a look. Initialize I implemented the interface on the ElwinModel but then I though it may be not necessary as its only use is for the mock. If you think is better practice I can change it.

[robertapplin]

Thanks for taking a look. Initialize I implemented the interface on the ElwinModel but then I though it may be not necessary as its only use is for the mock. If you think is better practice I can change it.

I think it probably would be best practise to use an interface class. That way it would be more consistent with how things are done for the presenters and views

[robertapplin]

Looks great! Adds a test for the Elwin presenter, and mocks out all dependencies for the presenter to make sure we are only testing the presenter - great job!