Unique validator for packaging metadata (BugFix)

[fernando79513]

Description

This PR is a follow up of #909. We were missing a check during the validation phase to make sure that there are not repeated packages in the packaging metadata files.

For that purpose, we have used the UniqueValueValidator for the Depends, Recommends and Suggests fields of the packaging metadata units, so they can't be repeated.

This change is not probable to make any break in previous versions, but it is possible if some package metadata units were using the same package twice.

Resolved issues

Closes CHECKBOX-1062

Documentation

Updated packaging-meta-data.rst

Tests

To run the new packaging tests:

cd ~/checkbox/checkbox-ng
python3 -m pytest -k PackagingUnitFieldValidationTests

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (1cf70e8) 37.50% compared to head (df6635b) 37.59%.
Report is 5 commits behind head on main.

Files	Patch %	Lines
checkbox-ng/plainbox/impl/unit/packaging.py	94.00%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #920      +/-   ##
==========================================
+ Coverage   37.50%   37.59%   +0.09%     
==========================================
  Files         313      313              
  Lines       34809    34835      +26     
  Branches     5983     5987       +4     
==========================================
+ Hits        13055    13097      +42     
+ Misses      21174    21154      -20     
- Partials      580      584       +4     

Flag	Coverage Δ
checkbox-ng	63.26% <94.11%> (+0.17%)	⬆️

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[kissiel]

This change is not probable to make any break in previous versions, but it is possible if some package metadata units were using the same package twice.

So we went from unpredictable behavior, to a predictable one. Having two units like that is/was a problem, so if we're breaking something with your changes, we really are just shedding light on the problem. I wouldn't go as far as calling it a breaking change.

[fernando79513]

This change is not probable to make any break in previous versions, but it is possible if some package metadata units were using the same package twice.

So we went from unpredictable behavior, to a predictable one. Having two units like that is/was a problem, so if we're breaking something with your changes, we really are just shedding light on the problem. I wouldn't go as far as calling it a breaking change.

Okey, I will change it to "BugFix" then

[kissiel]

If I understand the code correctly, the "Depends" field in the meta were capitalized because they are one-offs (type-like). But the code proposed here adds properties based on that section name (Capitalized), so the field name should be lowercase.

[kissiel]

Thanks for the explanations. This warrants a +1 now.