I don't know how to reproduce this issue in a test, so no tests for now.
Nonetheless, this fixes the issue for me at least on one map:
https://osu.ppy.sh/beatmapsets/1899665#taiko/3915653
This workaround is similar to #16475 (the test from that commit got
eventually removed for some reason).
In the visual test browser, if two `TestResultsWithPlayer` test cases
are ran consecutively, the second would die on `SoloStatisticsWatcher`
seeing duplicated online score IDs. This surfaced after
6ef39b87fe, which changed
`TestResultsScreen` to inherit `SoloResultsScreen` rather than
`ResultsScreen`.
This is probably _not_ a very good fix, but I'm trying to be pragmatic
for now. `SoloStatisticsWatcher` should probably not live in
`OsuGameBase`.