Currently we have fully implemented all normalization options for both $score and $scoreFusion. We also have tests for $score inside input pipelines in $scoreFusion.

We have not, however, tested putting a $score inside a $scoreFusion with different normalization options for $score ($sigmoid and $minMaxScaler); all of them currently have $score's normalization as "none".

Furthermore, we should add these test with different normalization options to the outer $scoreFusion as well.

So the different combinations we should consider are:

$scoreFusion: {
  pipelines: {
    p1: {$score: {score: ..., normalizeFunction: "sigmoid"}},
    p2: ...
  }
  normalization: "none"
}

$scoreFusion: {
  pipelines: {
    p1: {$score: {score: ..., normalizeFunction: "minMaxScaler"}},
    p2: ...
  }
  normalization: "none"
} 

$scoreFusion: {
  pipelines: {
    p1: {$score: {score: ..., normalizeFunction: "sigmoid"}},
    p2: ...
  }
  normalization: "sigmoid"
}

$scoreFusion: {
  pipelines: {
    p1: {$score: {score: ..., normalizeFunction: "minMaxScaler"}},
    p2: ...
  }
  normalization: "sigmoid"
} 

$scoreFusion: {
  pipelines: {
    p1: {$score: {score: ..., normalizeFunction: "sigmoid"}},
    p2: ...
  }
  normalization: "minMaxScaler"
} 

$scoreFusion: {
  pipelines: {
    p1: {$score: {score: ..., normalizeFunction: "minMaxScaler"}},
    p2: ...
  }
  normalization: "minMaxScaler"
} 

We should also set the scoreDetails to true for a some of these combinations and add them to score_fusion_score_details_test.js

Note: In SERVER-104742 we found that there were issues in sharded clusters with how the pipeline was split with respect to $_internalSetWindowFields (this is inserted with $minMaxScaler normalization on $scoreFusion). The solution was to push some $addFields stages (for rawScore and scoreDetails) before the $_internalSetWindowFields. We should watch out for the same situation when $minMaxScaler normalization is set in $score.