feat(metrics): add aggregateResultsByModule function

[nicojs]

aggregateResultsByModule [(Record<string, MutationTestResult>) => MutationTestResult]

Aggregates multiple reports together into a single report, grouped by module.

Input: resultsByModule The MutationTestResult objects by module name.

Closes #1180

[hugo-vrijswijk]

Some small comments about the code. But we've also talked about adding another possible field in the schema to allow multiple full reports aggregated inside a single schema (with different thresholds, configs, etc). How does that relate to this? I wouldn't want to merge this and expose it as a public API if we're going to make a very similar functionality soon as well

[hugo-vrijswijk]

What if an empty object is passed to the function? This Object.create thing makes me worry it gives unexpected results

[nicojs]

Object.create(null) is the emptiest object there is. Even more empty than {}, since it won't even have Object.prototype as its prototype

[hugo-vrijswijk]

Does {} give a different result?

[nicojs]

Of course 😌. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/create#custom_and_null_objects

[hugo-vrijswijk]

Then that should probably also have a test, right? {} seems a lot more common 🤔

[nicojs]

Good point. Added the test

[nicojs]

But we've also talked about adding another possible field in the schema to allow multiple full reports aggregated inside a single schema (with different thresholds, configs, etc).

I still want that, but I don't want to spend the time for that a.t.m. I actually just want the merging of tests files in the dashboard, and wanted to move that out of the dashboard because users are asking for it as well.

How does that relate to this? I wouldn't want to merge this and expose it as a public API if we're going to make a very similar functionality soon as well

When that functionality lands, I would expect the internals of this function to change so it provides the new format.

[hugo-vrijswijk]

@nicojs What is the current status of this PR?

[nicojs]

I forgot about it 😶

[hugo-vrijswijk]

Ship it!