diff --git a/ops/testing.py b/ops/testing.py
index 503a1f59b..882d8b07d 100644
--- a/ops/testing.py
+++ b/ops/testing.py
@@ -971,8 +971,7 @@ def _emit_relation_broken(self, relation_name: str, relation_id: int,
         app = self._model.get_app(remote_app)
         self._charm.on[relation_name].relation_broken.emit(relation, app)
 
-    def add_relation_unit(self, relation_id: int, remote_unit_name: str,
-                          data: Optional[Mapping[str, str]] = None) -> None:
+    def add_relation_unit(self, relation_id: int, remote_unit_name: str) -> None:
         """Add a new unit to a relation.
 
         This will trigger a `relation_joined` event. This would naturally be
@@ -993,7 +992,6 @@ def add_relation_unit(self, relation_id: int, remote_unit_name: str,
         Args:
             relation_id: The integer relation identifier (as returned by :meth:`add_relation`).
             remote_unit_name: A string representing the remote unit that is being added.
-            data: A str:str mapping to put in the unit's databag.
         """
         self._backend._relation_list_map[relation_id].append(remote_unit_name)
         # we can write remote unit data iff we are not in a hook env
@@ -1027,9 +1025,6 @@ def add_relation_unit(self, relation_id: int, remote_unit_name: str,
         self._charm.on[relation_name].relation_joined.emit(
             relation, remote_unit.app, remote_unit)
 
-        if data is not None:
-            self.update_relation_data(relation_id, remote_unit_name, data)
-
     def remove_relation_unit(self, relation_id: int, remote_unit_name: str) -> None:
         """Remove a unit from a relation.
 
diff --git a/test/test_model.py b/test/test_model.py
index 303d7b707..fba11a284 100644
--- a/test/test_model.py
+++ b/test/test_model.py
@@ -282,8 +282,11 @@ def test_remote_units_get_from_div_app(self):
             app_data={"app": "data"},
             unit_data={"unit": "data"}
         )
-        self.harness.add_relation_unit(relation_id, 'remoteapp/1', data={"some": "other"})
-        self.harness.add_relation_unit(relation_id, 'remoteapp/2', data={"some": "yams"})
+        self.harness.add_relation_unit(relation_id, 'remoteapp/1')
+        self.harness.add_relation_unit(relation_id, 'remoteapp/2')
+
+        self.harness.update_relation_data(relation_id, "remoteapp/1", {"some": "other"})
+        self.harness.update_relation_data(relation_id, "remoteapp/2", {"some": "yams"})
 
         rel_db1 = self.ensure_relation('db1')