Add tests to UserDeleteView endpoint

[Oksamies]

[!WARNING] This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite. Learn more

• #935 👈
• #934 : 1 other dependent PR (#937 )
• #1024
• #1025
• #1023
• #1044
• #1043
• master

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

:exclamation: No coverage uploaded for pull request base (add-delete-user-endpoint@67fb284). Click here to learn what that means.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## add-delete-user-endpoint #935 +/- ## =========================================================== Coverage ? 92.69% =========================================================== Files ? 279 Lines ? 8301 Branches ? 777 =========================================================== Hits ? 7695 Misses ? 500 Partials ? 106 ```

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