Use jest-matchers for assertions instead of expect

[skovhus]

Currently [email protected] is being integrated into Jest (see more background in jestjs/jest#1679).

In jest-codemods I'm working on a codemod to automate the process of going from mjackson/expect to jest-matchers (if running in a browser) or plain Jest (if running in node). 🤖

I've tested the codemod on this project and everything should still work.

Let me know what you think.

Blocked: currently fails in older browsers 💣

Seems like jest-matchers have untranspiled code SyntaxError: Unexpected keyword 'const'. Const declarations are not supported in strict mode..

Will look into a solution for this.

[timdorr]

There was talk of turning off some browser tests. @pshrmn did a trial run in #4884, but we haven't actually implemented it yet. We could probably stand to review the browser set too.

[timdorr]

And for the browser-based tests, those run on karma and mocha, so should we be switching to jest-matchers (which are presumably built for node) for tests that need a DOM anyways?

[skovhus]

If you want node test you can basically just run Jest (that internally sets up Jest matchers). I can do another PR showing this... will remove a lot of confirguration.

[timdorr]

Well, it's more that I'm thinking this should only apply to DOM-less packages (react-router, react-router-native, react-router-redux, react-router-config). Basically everything except react-router-dom.

[mjackson]

I'd love to just convert everything over to using Jest and ditch all of our custom karma + (flaky) BrowserStack integration. The history package should provide an abstraction over any behavior that requires browser-specific tests.

[timdorr]

I'd be totally down with that. react-router-redux already uses it and it works great.

[mjackson]

I converted all our tests to use Jest in 172dc16. Thanks for the push here, @skovhus :) I relied on some of the code in this PR to know how to do the conversions.

[skovhus]

@mjackson glad to hear this and thanks for letting me use this repo for testing jest-codemods. ; )