fix(mappers): Schema passthrough for whitelisted fields

[edgarrmondragon]

Related:

• Invalid schema when modifying an existing property in place MeltanoLabs/meltano-map-transform#30
• Mapper assumes wrong schema when just whitelisting fields MeltanoLabs/meltano-map-transform#66

We'll have to release a new version of the SDK, and bump it in MeltanoLabs/meltano-map-transform.

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I changed the test_mapped_stream to use snapshots so we can validate the entire tap output.

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📚 Documentation preview 📚: https://meltano-sdk--1219.org.readthedocs.build/en/1219/

[codecov]

Codecov Report

Merging #1219 (61469de) into main (417e75a) will increase coverage by 0.04%.
The diff coverage is 100.00%.

❗ Current head 61469de differs from pull request most recent head f43369f. Consider uploading reports for the commit f43369f to get more accurate results

@@            Coverage Diff             @@
##             main    #1219      +/-   ##
==========================================
+ Coverage   83.68%   83.72%   +0.04%     
==========================================
  Files          42       42              
  Lines        3910     3909       -1     
  Branches      666      665       -1     
==========================================
+ Hits         3272     3273       +1     
  Misses        473      473              
+ Partials      165      163       -2     

Impacted Files	Coverage Δ
singer_sdk/helpers/_typing.py	52.79% <100.00%> (+0.32%)	⬆️
singer_sdk/streams/core.py	85.74% <0.00%> (+0.24%)	⬆️

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[aaronsteers]

@edgarrmondragon - This is great.

I like this approach a lot, but the library is new to me and I'm not sure if I would know where to look to confirm the changes. So, if we fix the double-state messages at the end of each sync (for example), I expect the job would fail. And I think (?) then the proper course for developer would then be to run a snapshot update, then confirm the git diff of those snapshots that got updated, and if the new schema files are better or at least as good, then those could be merged back to main.

Could we add something in CONTRIBUTING.md about the snapshots feature and how they should be maintained/updated?

Thanks!

[edgarrmondragon]

Could we add something in CONTRIBUTING.md about the snapshots feature and how they should be maintained/updated?

@aaronsteers I've updated the contributing page with more details: af1ef39, https://meltano-sdk--1219.org.readthedocs.build/en/1219/CONTRIBUTING.html#snapshot-testing