fix(application): attrs & tests for build planner

[lengau]

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• Have you successfully run tox run -e test-py310? (supported versions: py39, py310, py311, py312)

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[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (6ff3e0b) 88.83% compared to head (8d2ee23) 88.88%.
Report is 6 commits behind head on feature/craft-application.

Files	Patch %	Lines
snapcraft/application.py	88.23%	2 Missing ⚠️

Additional details and impacted files

@@                      Coverage Diff                      @@
##           feature/craft-application    #4588      +/-   ##
=============================================================
+ Coverage                      88.83%   88.88%   +0.04%     
=============================================================
  Files                            327      329       +2     
  Lines                          22033    22053      +20     
=============================================================
+ Hits                           19573    19601      +28     
+ Misses                          2460     2452       -8     

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[mr-cal]

Tests are very well written.

[tigarmo]

@lengau I think this is still broken (from the spread tests):

2024-02-20T15:08:47.5728588Z 2024-02-20 15:08:47 Error executing google:ubuntu-22.04-64:tests/spread/core24/architectures:env_var_match (feb201506-275200) : 
2024-02-20T15:08:47.5730645Z -----
2024-02-20T15:08:47.5731243Z + cd ./snaps/env-var-match
2024-02-20T15:08:47.5747095Z + [[ -e environmental-variables.txt ]]
2024-02-20T15:08:47.5748802Z ++ cat environmental-variables.txt
2024-02-20T15:08:47.5750465Z + eval 'SNAPCRAFT_BUILD_FOR="arm64"' snapcraft pack --destructive-mode
2024-02-20T15:08:47.5752717Z ++ SNAPCRAFT_BUILD_FOR=arm64
2024-02-20T15:08:47.5753514Z ++ snapcraft pack --destructive-mode
2024-02-20T15:08:47.5755936Z snapcraft internal error: ValidationError(model='SnapcraftBuildPlanner', errors=[***'loc': ('architectures',), 'msg': "every item must either be a string or an object for [***'build-on': 'amd64', 'build-for': 'amd64'***, ***'build-on': ['amd64', 'arm64'], 'build-for': 'arm64'***]", 'type': 'value_error'***])

[syu-w]

Not sure what happened, now spread: command not found

[tigarmo]

Thanks! I mostly looked at the spread tests and I think the failures are all expected/unrelated