experimental: add a hacky helper to import "original/shadowed" modules from within overlays

my/util/hpi_heartbeat.py

@@ -0,0 +1,54 @@
+"""
+Just an helper module for testing HPI overlays
+In particular the behaviour of import_original_module function
+
+The idea of testing is that overlays extend this module, and add their own
+items to items(), and the checker asserts all overlays have contributed.
+"""
+from my.core import __NOT_HPI_MODULE__
+
+from dataclasses import dataclass
+from datetime import datetime
+import sys
+from typing import Iterator, List
+
+NOW = datetime.now()
+
+
+@dataclass
+class Item:
+    dt: datetime
+    message: str
+    path: List[str]
+
+
+def get_pkg_path() -> List[str]:
+    pkg = sys.modules[__package__]
+    return list(pkg.__path__)
+
+
+# NOTE: since we're hacking path for my.util
+# imports from my. should work as expected
+# (even though my.config is in the private config)
+from my.config import demo
+
+assert demo.username == 'todo'
+
+# however, this won't work while the module is imported
+# from my.util import extra
+# assert extra.message == 'EXTRA'
+# but it will work when we actually call the function (see below)
+
+
+def items() -> Iterator[Item]:
+    from my.config import demo
+
+    assert demo.username == 'todo'
+
+    # here the import works as expected, since by the time the function is called,
+    # all overlays were already processed and paths/sys.modules restored
+    from my.util import extra  # type: ignore[attr-defined]
+
+    assert extra.message == 'EXTRA'
+
+    yield Item(dt=NOW, message='hpi main', path=get_pkg_path())