fix: export default in test environments

[mrazauskas]

Summary

Really nice that Jest 27 allows to write custom environments in TypeScript (#8751). I was playing with it. All works really well. Thanks!

Just a detail. Imports look clumsy in TS – import NodeEnvironment = require('jest-environment-node'). Perhaps export default could be used instead of export =? This way TS and MJS imports look good, but a breaking change for CJS users is introduced. Is there a better solution?

(Alternatively TS uses can set "esModuleInterop": true, but this isn’t elegant.)

Test plan

Existing tests are updated.

[SimenB]

Problem with default export now is that it's not actually ESM, so native ESM must do

import TestEnv from 'jest-environment-node';

export default MyTestEnv extends TestEnv.default {}

Using a named import (or native ESM) is better... Might go for wannabe ESM for Jest 27, then convert to native ESM for Jest 28

[mrazauskas]

Might go for wannabe ESM for Jest 27, then convert to native ESM for Jest 28

You see it better. I was thinking, Jest 27 most probably will be build as CJS. At the same time, ESM for test environment will be supported (#11033). export default is alright for a library in transition.

One test is now failing. Is it really related with my PR? Seemed like all was good before. Can’t figure out what happened.

[github-actions]

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