fix: import caldav.testing.registry on its own

caldav/testing/base.py

@@ -639,13 +639,3 @@ def is_accessible(self) -> bool:
                 return True
         except (OSError, ValueError):
             return False
-
-
-# Deferred registration to avoid circular imports
-def _register_external_server() -> None:
-    from .registry import register_server_class
-
-    register_server_class("external", ExternalTestServer)
-
-
-_register_external_server()

caldav/testing/registry.py

@@ -33,10 +33,12 @@
 
 import os
 
-from .base import TestServer
+from .base import ExternalTestServer, TestServer
 
-# Server class registry - maps type names to server classes
-_SERVER_CLASSES: dict[str, type[TestServer]] = {}
+# Server class registry - maps type names to server classes.  The external
+# class is registered here rather than in base, which must not import this
+# module: base is imported first, from here.
+_SERVER_CLASSES: dict[str, type[TestServer]] = {"external": ExternalTestServer}
 
 
 def register_server_class(type_name: str, server_class: type[TestServer]) -> None:

tests/test_testing_base.py

@@ -348,3 +348,30 @@ def test_test_servers_submodules_are_package_attributes(monkeypatch) -> None:
     assert tests.test_servers.base is base
     monkeypatch.setattr("tests.test_servers.base.DEFAULT_HTTP_TIMEOUT", 1)
     assert base.DEFAULT_HTTP_TIMEOUT == 1
+
+
+@pytest.mark.parametrize(
+    "module",
+    [
+        "caldav.testing",
+        "caldav.testing.base",
+        "caldav.testing.config_loader",
+        "caldav.testing.docker",
+        "caldav.testing.embedded",
+        "caldav.testing.helpers",
+        "caldav.testing.registry",
+    ],
+)
+def test_each_testing_module_imports_on_its_own(module: str) -> None:
+    """A consumer may import any submodule first; none may depend on another having been imported."""
+    import os
+    import subprocess
+    import sys
+
+    import caldav
+
+    # This checkout's caldav, not whatever the editable install points at (a worktree's main checkout)
+    root = str(Path(caldav.__file__).resolve().parent.parent)
+    env = {**os.environ, "PYTHONPATH": os.pathsep.join([root, os.environ.get("PYTHONPATH", "")])}
+    code = f"import {module}; from caldav.testing.registry import get_server_class; assert get_server_class('external')"
+    subprocess.run([sys.executable, "-c", code], check=True, cwd=root, env=env)