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Also add ts-jest and npm-run-all.
After this updates I will start working on #1111

There's a bit too much happening in this PR. do you mind separating out the stuff unrelated to package.json dependencies and yarn.lock?

Specifically the ts-jest changes are controversial and reduce test coverage, so I'd like to discuss those in isolation

There's a bit too much happening in this PR. do you mind separating out the stuff unrelated to package.json dependencies and yarn.lock?

Yep. Sorry, I just can't stop sometimes.

dist/immutable.min.js changed because of uglify-js update

Specifically the ts-jest changes are controversial and reduce test coverage, so I'd like to discuss those in isolation

Oh, it was recommended in jest readme so i thought it's ok.