fix: CSV upload with overprescribed table/schema

[john-bodley]

SUMMARY

This PR fixes a couple of issues related to CSV upload:

1. If the schema was overprescribed (both explicitly and in the table name) the flashed message would fail (resulting in a 500 error) due to invalid field names passed to the message generator. This code path was not covered by unit tests.
2. The schema was not correctly extracted when specified in the table name.

I debated how best to tackle this and initially went down the route of redefining the server-side form post logic (with unit tests), but opted for hopefully an easier/cleaner route by adding form validators.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

Tested locally.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #18758 (644bca6) into master (cf8b57e) will decrease coverage by 0.15%.
The diff coverage is 70.96%.

❗ Current head 644bca6 differs from pull request most recent head a424b6d. Consider uploading reports for the commit a424b6d to get more accurate results

@@            Coverage Diff             @@
##           master   #18758      +/-   ##
==========================================
- Coverage   66.31%   66.15%   -0.16%     
==========================================
  Files        1620     1620              
  Lines       63080    63066      -14     
  Branches     6370     6370              
==========================================
- Hits        41832    41722     -110     
- Misses      19591    19687      +96     
  Partials     1657     1657              

Flag	Coverage Δ
hive	?
mysql	81.45% <100.00%> (+0.02%)	⬆️
postgres	81.49% <100.00%> (+0.02%)	⬆️
presto	?
python	81.58% <100.00%> (-0.32%)	⬇️
sqlite	81.18% <100.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...frontend/src/SqlLab/components/ResultSet/index.tsx	50.73% <ø> (ø)
superset-frontend/src/views/App.tsx	0.00% <0.00%> (ø)
superset/config.py	91.92% <ø> (ø)
superset/initialization/__init__.py	90.65% <ø> (+0.45%)	⬆️
superset/views/database/views.py	91.89% <ø> (+3.43%)	⬆️
...board/components/nativeFilters/FilterBar/index.tsx	69.82% <50.00%> (ø)
...perset-frontend/src/views/components/MenuRight.tsx	80.48% <60.00%> (ø)
superset-frontend/src/views/components/Menu.tsx	55.26% <77.77%> (ø)
...s/legacy-plugin-chart-country-map/src/countries.ts	100.00% <100.00%> (ø)
...rset-frontend/src/components/DeleteModal/index.tsx	84.21% <100.00%> (ø)
... and 16 more

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[john-bodley]

This was the initial error. The csv_table.table and csv_table.schema variables are not inputs to the function.

[ad-m]

This is a detail, but I think it is worth moving the format checking to a separate method / function, so that the name of the method says what you really want to check and hide the implementations here to improve readability. It currently says you want to check if it contains a period, but in fact you are checking to see if it contains a namespace.

[john-bodley]

@ad-m I've restructured the PR using an alternative formulation.

[craig-rueda]

Can we add a test to make sure this bit ends up being covered?

[john-bodley]

@craig-rueda I initially (and wrongfully) thought the WTForms validation logic was all frontend and would be difficult to capture in a unit test but it's all server side and thus a backend unit test is viable. I've added the test as requested.