chore(website): improve docs around jest testing

[Weakky]

closes #1218
relates to https://github.com/graphql-nexus/nexus/issues/1217#issuecomment-663459021

I surprisingly can't find any issue about the underlying problem. This fixes the testing component, which wasn't able to run tests whenever there was a type error. That would happen fairly often right after installing Jest for instance, which deletes all the generated types. It should also fix the tutorial.

TODO

• docs
  • jsdoc
  • website api
  • website guides
  • website tutorial
• tests

[jasonkuhrt]

@Weakky maybe make a follow up PR where the diagnostics are only disabled in development. In CI, I don't think we would want that setting. Thoughts?

[luhagel]

I had the error two days ago(same message, different cause), and only fixed it after single stepping through the debugger.

What happened on my end was that the reflection would fail, but the result was never logged out, nor was there any indication that it was failing because of that.

In my my case the test env was missing a proper dotenv setup and my initial validation failed when the app.ts was run/reflected upon.

All in all, getting failed reflection results shown to the user would solve a lot of these issues I think

[jasonkuhrt]

All in all, getting failed reflection results shown to the user would solve a lot of these issues I think

Agreed 💯

Will create an issue for it now.