[IMPROVEMENT] Categorize existing validation test cases

[nitbharambe]

Describe the problem

Currently we have many test cases in validation (>50 or so for each). We have smaller number of tests for modelling while bugs or minimal cases regarding investigation and features account a significant count.

Its easy to forget why a test case was created because the title cannot fully describe the reason.

Improvement proposal

Let us categorize these tests into relevant categories:

• Modelling validation cases
• Error handling cases
• Minimal cases
• Feature related test

And more categories if appropriate. This task would only involve moving cases to new subfolders

[mgovers]

would the parent repo structure remain the same? e.g.

- tests/data/
  - power_flow/
    - modeling_validation/
    - error_handling/
    - ...
  - state_estimation/
    - ...
  - short_circuit/
    - ...

and how do we deal with the existing subfolders like automatic_tap_changer? Not a big issue and it should be easy to handle but would like to make a choice before we start with this.

[figueroa1395]

Also, we can potentially add a readme.mdto each test folder to explicitly explain what is what on each case.

[nitbharambe]

would the parent repo structure remain the same? e.g.

We keep tests/data/power_flow and tests_Data/state_estimation same. Anything else would require changes in the handling of validation. (Which we are going to anyway, hence open to ideas)

and how do we deal with the existing subfolders like automatic_tap_changer? Not a big issue and it should be easy to handle but would like to make a choice before we start with this.

We can divide existing subfolders if it has multiple of a category. But I imagine that is not the case in most places.