Add more testing for online ranking

[dtinth]

Add a bunch of more black-box testing for the online ranking system.

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov-commenter]

Codecov Report

Base: 86.49% // Head: 86.51% // Increases project coverage by +0.02% :tada:

Coverage data is based on head (9d27880) compared to base (07f0d4f). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #824 +/- ## ========================================== + Coverage 86.49% 86.51% +0.02% ========================================== Files 178 178 Lines 5353 5362 +9 Branches 363 363 ========================================== + Hits 4630 4639 +9 Misses 673 673 Partials 50 50 ``` | [Impacted Files](https://codecov.io/gh/bemusic/bemuse/pull/824?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bemusic) | Coverage Δ | | |---|---|---| | [bemuse/src/rules/mapping-mode.ts](https://codecov.io/gh/bemusic/bemuse/pull/824?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bemusic#diff-YmVtdXNlL3NyYy9ydWxlcy9tYXBwaW5nLW1vZGUudHM=) | `100.00% <ø> (ø)` | | | [...ne/scoreboard-system/createFakeScoreboardClient.ts](https://codecov.io/gh/bemusic/bemuse/pull/824?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bemusic#diff-YmVtdXNlL3NyYy9vbmxpbmUvc2NvcmVib2FyZC1zeXN0ZW0vY3JlYXRlRmFrZVNjb3JlYm9hcmRDbGllbnQudHM=) | `79.16% <100.00%> (+2.97%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bemusic). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bemusic)

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