Expect Type Error #31
Description
Hey and thanks for this lib - I started using it to day, coming from using plain .ts files with typed variable assignments & forced errors with // @ts-expect-error on top. It worked well, but I want to get to something more structured.
I see I also have to use // ts-expect-error to catch expected errors in ts-expect-error, which is fine.
I'm also in the habit of documenting the expected errors, like we do in out code tests, but it's purely for documentation & future reference, as it's not possible to be checked. For example:
const identity = <T>(val: T): T => val
// @ts-expect-error: TS2322: Type number is not assignable to type string
const str: string = identity(123)
In ts-expect we have the expectType<number>("test"); // Compiler error example, but we don't document the error somehow, so it can be checked.
An exotic new version could support something like:
expectTypeError<number>("test", `TS2345: Argument of type string is not assignable to parameter of type number`);
and perhaps do some magic to obtain error codes & descriptions.
I know this is much much harder, and probably not just a lib, as it perhaps would have to incorporate information from the IDE or TS compiler to do the trick, but there might be a way ;-) Maybe an IDE plugin? Who knows!
Anyway, just a thought, just sharing!
Activity
anodynos commentedon Mar 10, 2024
Having used it for a whole day, I want to add another issue.
I find the strict version of
much more useful than simple
expectType, but when it fails during development it doesn't show the real error, instead it only showsTS2345: Argument of type true is not assignable to parameter of type false.I resort to assignment to a variable, which is not always desirable... I think if this is fixed in will make the library 5x more useful!
blakeembrey commentedon Mar 10, 2024
Definitely agree with both of these, and I'll keep them in mind if anyone else wants to work on it or I find time, but I think they both require hooking into the TypeScript compiler directly.
Another option might be: https://github.com/tsdjs/tsd
It's much more complete and uses the compiler IIRC, so probably covers these cases already.
mrazauskas commentedon Nov 23, 2024
@anodynos Please take a look at TSTyche (this my project), https://github.com/tstyche/tstyche. It has the
.toRaiseError(), which is able to capture type error:By the way, a better idea to test assignably would be using
.not.toBeAssignableTo().anodynos commentedon Nov 24, 2024
Thank you @mrazauskas, it looks interesting, I will have a look at it when I have time for my projects - for now I'm heavily using
expectTypeand the gang, eg https://github.com/NeoZen-dev/neozen-tools/blob/78604a935ec95357db2f65c5e115893883a67ccf/packages/zen/src/code/loopzen/__tests__/all-typings/master/Master-typings-spec.masterTemplate.ts#L307mrazauskas commentedon Nov 24, 2024
@anodynos Thanks for sharing your project!
To add few more details, I was developing TSTyche to be able to test types of a project that had more than 1000 assertions (in a monorepo with more than 20 packages). At this scale I wanted to be able:
.onlyand.skip,TSTyche can do all this (and more!). At any scale (;
It works with any generic type assertion library as well. You can use TSTyche with
ts-expect, for example. But beware thatTypeEqualofts-expectdoes not take into account TypeScript compiler’s options likeexactOptionalPropertyTypes, playground: