`TestSceneScoring` included a local simulation of stable's Score V1
algorithm. One of the parts of said algorithm is a mysterious
"score multiplier", influenced by - among others - the beatmap's drain
rate, overall difficulty, circle size, object count, drain length,
and active mods. (An implementation of this already exists in lazer
source, in `OsuLegacyScoreSimulator`, but more on this later.)
However, `TestSceneScoring` had this multiplier in _two_ places, with
_two_ distinct values, one of which being 1 (i.e. basically off).
Unfortunately, the place that had 1 as the multiplier was the wrong one.
Stable calculates the score increase for every hit in two stages;
first, it takes the raw numerical value of the judgement, but then
applies a combo-based bonus on top of it:
scoreIncrease += (int)(Math.Max(0, ComboCounter.HitCombo - 1) * (scoreIncrease / 25 * ScoreMultiplier));
On the face of it, it may appear that the `ScoreMultiplier` factor
can be factored out and applied at the end only when returning total
score. However, once the above formula is rewritten as:
scoreIncrease = scoreIncrease + (int)(Math.Max(0, ComboCounter.HitCombo - 1) * (scoreIncrease / 25 * ScoreMultiplier));
= scoreIncrease * (1 + (Math.Max(0, ComboCounter.HitCombo - 1) / 25 * ScoreMultiplier))
it becomes clear that that assumption is actually _incorrect_,
and the `ScoreMultiplier` _must_ be applied to every score increase
individually.
The above was cross-checked experimentally against stable source
on an example test map with 100 objects, and a replay hitting them
perfectly.
To be fair, currently the test is a bit pointless (as it has no reason
to be a `SkinnableTestScene`, it gains precisely nothing from it - all
that is shown there is some generic components on song select). But that
is no worse then `master`, so look away for now.
These are tested framework-side to throw exceptions, but the
test is ignored for the source generated version because it quietly
allows this scenario.
The source gen project should eventually have an analyser for these
unsupported cases, or we could consider relaxing this particular case.
