Migrate typescript tests to use tstyche

[vkarpov15]

Prerequisites

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Issue

Re: discussion from #15951, tstyche looks like a great tool for running the sort of TypeScript tests that we used tsd for. I'm opening up a separate issue for this since I don't want to merge #15951 first

[mrazauskas]

Happy to see this idea. I can open a PR next week unless you have already started to work on it.

[vkarpov15]

I haven't started working on this, so feel free to take a pass at it if you have the time 👍

[AbdelrahmanHafez]

While working on #15965 I noticed that the current ExpectType setup doesn't catch any, which means type regression tests can silently pass.

For example, if a function is supposed to return { title: string } but regresses to { [key: string]: any }, this test passes without errors:

ExpectType<string>(obj.title); // passes, because obj.title is `any` and `any` is assignable to `string`

We only caught the regression by using this pattern instead:

// @ts-expect-error title should be string, not any
const _check: number = obj.title;

This works because when obj.title is string, the assignment to number fails (and @ts-expect-error suppresses it). But when obj.title is any, the assignment succeeds, making the @ts-expect-error directive unused, which is a compile error.

[mrazauskas]

I also saw few places where ExpectType is not catching never. It can be I mixed up something with setup or so.

For the beginning I wanted to introduce TSTyche for checking // @ts-expect-error messages. (Working on a PR.) I think that would be a good first step.