added default juju data to default remote unit databag

scenario/state.py

@@ -444,6 +444,14 @@ def broken_event(self) -> "Event":
         )
 
 
+_DEFAULT_IP = "42.42.42.42"
+DEFAULT_JUJU_DATABAG = {
+    "egress-subnets": _DEFAULT_IP,
+    "ingress-address": _DEFAULT_IP,
+    "private-address": _DEFAULT_IP,
+}
+
+
 @dataclasses.dataclass(frozen=True)
 class Relation(RelationBase):
     remote_app_name: str = "remote"
@@ -453,7 +461,7 @@ class Relation(RelationBase):
 
     remote_app_data: "RawDataBagContents" = dataclasses.field(default_factory=dict)
     remote_units_data: Dict["UnitID", "RawDataBagContents"] = dataclasses.field(
-        default_factory=lambda: {0: {}},
+        default_factory=lambda: {0: DEFAULT_JUJU_DATABAG.copy()},  # dedup
     )
 
     @property

tests/test_e2e/test_relations.py

@@ -5,6 +5,8 @@
 from ops.framework import EventBase, Framework
 
 from scenario.state import (
+    _DEFAULT_IP,
+    DEFAULT_JUJU_DATABAG,
     PeerRelation,
     Relation,
     RelationBase,
@@ -229,6 +231,44 @@ def callback(charm: CharmBase, event):
     )
 
 
+@pytest.mark.parametrize(
+    "evt_name",
+    ("changed", "broken", "departed", "joined", "created"),
+)
+def test_relation_events_remote_units_data_defaults(mycharm, evt_name, caplog):
+    relation = Relation(
+        endpoint="foo",
+        interface="foo",
+    )
+
+    def callback(charm: CharmBase, event):
+        if isinstance(event, CollectStatusEvent):
+            return
+
+        assert event.app  # that's always present
+        remote_unit = event.relation.units.pop()
+
+        assert event.relation.data[remote_unit] == DEFAULT_JUJU_DATABAG
+
+    mycharm._call = callback
+
+    trigger(
+        State(
+            relations=[
+                relation,
+            ],
+        ),
+        getattr(relation, f"{evt_name}_event"),
+        mycharm,
+        meta={
+            "name": "local",
+            "requires": {
+                "foo": {"interface": "foo"},
+            },
+        },
+    )
+
+
 @pytest.mark.parametrize(
     "evt_name",
     ("changed", "broken", "departed", "joined", "created"),