Summary

It looks like the empty.d.ts file in type tests does nothing. I think it can be removed safely just to have less noise around.

Here is why. By design tsd is running type checks (or test) on .d.ts type definition files. Not on .ts source, but on .d.ts inside the build artefact. Here in jest repo the type tests are set up exactly like this – the build files are tested.

The empty.d.ts is unofficial work around to run tests on .ts files. The thing is that tsd needs to have have some .d.ts to work. Install tsd in an empty folder and run yarn tsd. It will throw: "The type definition index.d.ts does not exist. Create one and try again." If an empty index.d.ts is added, tsd will complain that it can’t find any test.

Now the interesting part – add a test, but keep index.d.ts empty. Error: "./index.d.ts is not a module." That’s right! It has no exports, because we kept it empty. Now look at empty.d.ts file in this repo. No exports. Seems like this even isn’t valid .d.ts. Or?

After playing more with tsd I think that empty.d.ts is redundant in this repo. Might be I missed something. So let’s check what CI thinks.

In general this PR changes nothing. It is just a clean up with very long explanation. Thanks for reading (;

Test plan

After removal all works as expected locally. I was running type test before and after the change with Jest’s cache cleaned and the result is the same. Here I included failing test to avoid false positive. On CI nothing should fail.