Create DAGNode in Core

[uranusjr]

This handles the DAGNode part for #52141.

Logic shared by both SDK and Core is implemented in a shared library. The shared class is implemented as a Generic, with concrete types (DAG, TaskGroup, etc.) supplied in Core and Task SDK.

I’m not sure what to do with tests… The functionalities are currently covered in SDK or Core tests. Do we pull them to the shared library? That would require us to add quite some code to stub out the concrete types that are unavailable in _shared.

[potiuk]

I’m not sure what to do with tests… The functionalities are currently covered in SDK or Core tests. Do we pull them to the shared library? That would require us to add quite some code to stub out the concrete types that are unavailable in _shared.

Which tests for example ?

[uranusjr]

For example airflow-core/tests/unit/models/test_dag.py::TestTaskClearingSetupTeardownBehavior::test_get_flat_relative_ids_with_setup

This test really just tests get_flat_relative_ids_with_setup works as expected. This functon is implemented in the shared lib in this PR, but you can’t test the function on its own without an operator class. The same goes for everything in the class (aside from very trivial ones such as get_dag() that don’t really need tests anyway), and the package ends up having no tests at all (and it currently fails CI).

[potiuk]

For example airflow-core/tests/unit/models/test_dag.py::TestTaskClearingSetupTeardownBehavior::test_get_flat_relative_ids_with_setup

I think those tests should remain as they are - they are testing effectively integration of the methods with actual instances of Dag/Task for example.

I think however we could have mocked versions of the classes that would not be created by Dag/ / make_tests instantitaiton but simply using MagicMock objects with spec ?

[uranusjr]

Redoing this in #59708.