fix: tolerate missing external import references

tests/test_references.py

@@ -0,0 +1,91 @@
+from netbox_export.services.references import MISSING_REFERENCE, ReferenceResolver
+
+
+class DoesNotExist(Exception):
+    pass
+
+
+class MultipleObjectsReturned(Exception):
+    pass
+
+
+class FakeManager:
+    def __init__(self, result):
+        self.result = result
+        self.calls = 0
+
+    def get(self, **lookup):
+        self.calls += 1
+        if isinstance(self.result, Exception):
+            raise self.result
+        return self.result
+
+
+def fake_model(manager):
+    return type(
+        "FakeModel",
+        (),
+        {
+            "DoesNotExist": DoesNotExist,
+            "MultipleObjectsReturned": MultipleObjectsReturned,
+            "_default_manager": manager,
+        },
+    )
+
+
+def test_missing_external_reference_is_omitted_and_warned_once():
+    manager = FakeManager(DoesNotExist())
+    model = fake_model(manager)
+    warnings = []
+    resolver = ReferenceResolver({}, warnings, lambda label: model)
+    spec = {"external": {"model": "users.user", "lookup": {"username": "lke"}}}
+
+    first, first_available = resolver.resolve(spec)
+    second, second_available = resolver.resolve(spec)
+
+    assert first is MISSING_REFERENCE
+    assert second is MISSING_REFERENCE
+    assert first_available is True
+    assert second_available is True
+    assert manager.calls == 1
+    assert warnings == [
+        "Externe Referenz ausgelassen: users.user mit {'username': 'lke'} (nicht gefunden)."
+    ]
+
+
+def test_ambiguous_external_reference_is_omitted():
+    manager = FakeManager(MultipleObjectsReturned())
+    model = fake_model(manager)
+    warnings = []
+    resolver = ReferenceResolver({}, warnings, lambda label: model)
+
+    value, available = resolver.resolve(
+        {"external": {"model": "users.group", "lookup": {"name": "NetBox"}}}
+    )
+
+    assert value is MISSING_REFERENCE
+    assert available is True
+    assert warnings == [
+        "Externe Referenz ausgelassen: users.group mit {'name': 'NetBox'} (nicht eindeutig)."
+    ]
+
+
+def test_reference_to_skipped_record_is_omitted_and_warned_once():
+    warnings = []
+    resolver = ReferenceResolver({}, warnings, lambda label: None)
+    resolver.skip("dcim.rackreservation:17", "dcim.rackreservation", ["user"])
+
+    first, first_available = resolver.resolve({"ref": "dcim.rackreservation:17"})
+    second, second_available = resolver.resolve({"ref": "dcim.rackreservation:17"})
+
+    assert first is MISSING_REFERENCE
+    assert second is MISSING_REFERENCE
+    assert first_available is True
+    assert second_available is True
+    assert warnings == [
+        (
+            "dcim.rackreservation:17 (dcim.rackreservation) wurde wegen fehlender "
+            "Pflichtreferenz übersprungen: user."
+        ),
+        "Referenzen auf das übersprungene Objekt dcim.rackreservation:17 wurden ausgelassen.",
+    ]