Ts-jest: Support Jest 26

[ahnpnl]

🚀 Feature Proposal

Jest 26 has released. We need to provide support for that.

Motivation

Make developers feel comfortable to work

TODO

• Set minimum required version of TypeScript to 3.8, example in https://github.com/kulshekhar/ts-jest/pull/1530
• Set jest version range for peerDependencies in root package.json.
• Update e2e templates' dependencies.
• Adjust codes to be compatible with Jest 26 in src/util/version-checker.ts and src/util/version-checker.spec.ts.
• Change node 8 Travis to node 12 and change node 12 Travis to node 14.
• Set prettier: 2.x, husky: 4.x, fs-extra: 9.x, semver: 7.x.
• Upgrade some jest dependencies.
• Set required minimum node@10 in package.json.
• Update dependencies for projects in e2e/__external-projects__

If you see other things, please provide us information.

[ahnpnl]

@kulshekhar should we separate 2 releases, with next branch target v25.5.0 and another branch target v26 ?

[kulshekhar]

@ahnpnl I'm not sure I understand the reason. Why would the next version be older that v26?

[ahnpnl]

actually my purpose is we separate 2 releases, as next branch will be merged into master first for release 25.5.0. After that this PR can land on next branch as for release 26.0.0.

I'm not sure if this approach is needed because there can be a situation that not all users can go immediately to jest 26 (which requires TypeScript 3.8). Currently 25.5.0-beta.0 (which is based on next branch) contains the most important change is performance boost for isolatedModules: false.

So IMO we should separate these 2 releases, as 25.5.0 goes first and 26.0.0 goes after that

[kulshekhar]

@ahnpnl that sounds good. I misunderstood earlier

[ahnpnl]

Close via #1597

[ahnpnl]

this feature will be in the next release 26.0.0, ETA somewhere next week.

[GoldFlsh]

Hello, just wondering if you still expect this this week?

[ahnpnl]

yes it is still on track :)

[GoldFlsh]

Yay!! :) thx for the update.

[ahnpnl]

FYI 26.0.0 was out last weekend