Add the LinkML meta-model to the test set

[Silvanoc]

What is your feature request?

Eating LinkML its own "dog-food" (LinkML meta-model is specified in LinkML), it would be meaningful to ensure that LinkML tooling works properly on the LinkML meta-model itself.

How important is this feature to you?

• Low - It improves test coverage, but does not provide any additional features to LinkML.

Additional context

Issue #2284 could have been detected running typical tests (like running gen-project) on the LinkML meta-model. See this comment for scoped testing.

[Silvanoc]

I have converted a feature request into a discussion, therefore the same structure.

[sneakers-the-rat]

i think we do this? https://github.com/linkml/linkml/blob/main/tests/test_base/test_metamodel.py

it's a weak test (snapshot test) but it does test that the generated python is valid. it misses #2284 because nothing in the metamodel uses an item from an enum as a default (as far as i can tell?)

[Silvanoc]

You are probably right. I oversaw it. What it is missing is the validation of the generated Python code 🙁 Therefore the tests could not detect issue #2284. So I suppose a small fix in test_metamodel.py should do it.