Duplicating Artist if Featured

[gcoppola19]

Description

Fixes #6166

(...)

Checking if an Artist is already present in featured, and not adding it from Discogs plug in

I didn't add chaneglog or documentation, and can do so, but wanted to make sure this was the intended usage and implementation.

• [ ] Documentation.
• [ ] Changelog. (Add an entry to docs/changelog.rst to the bottom of one of the lists near the top of the document.)
• [ x] Tests. (Very much encouraged but not strictly required.)

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 67.95%. Comparing base (2bd77b9) to head (0317ae1). :white_check_mark: All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6201      +/-   ##
==========================================
+ Coverage   67.93%   67.95%   +0.02%     
==========================================
  Files         137      137              
  Lines       18677    18690      +13     
  Branches     3155     3157       +2     
==========================================
+ Hits        12688    12701      +13     
  Misses       5324     5324              
  Partials      665      665              

Files with missing lines	Coverage Δ
beetsplug/discogs.py	71.70% <100.00%> (+0.92%)	:arrow_up:

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[Serene-Arc]

Hi, couple things:

• Why was a test file deleted?
• For anything regarding string parsing, I'd want a ton of tests for edge cases.