verify: The ops "How to manage actions" doc shows a snapshot action handler th

kepler/charmcraft.yaml

@@ -47,6 +47,17 @@ containers:
   demo-server:
     resource: demo-server-image
 
+actions:
+  snapshot:
+    description: Take a snapshot of the database.
+    params:
+      filename:
+        type: string
+        description: The name of the snapshot file.
+    required:
+      - filename
+    additionalProperties: false
+
 resources:
   # An OCI image resource for the container listed above.
   demo-server-image:

kepler/src/charm.py

@@ -31,6 +31,23 @@ def __init__(self, framework: ops.Framework) -> None:
         super().__init__(framework)
         self.pebble_service_name = "fastapi-service"
         framework.observe(self.on["demo-server"].pebble_ready, self._on_demo_server_pebble_ready)
+        framework.observe(self.on["snapshot"].action, self._on_snapshot_action)
+
+    def _on_snapshot_action(self, event: ops.ActionEvent) -> None:
+        """Handle the snapshot action, mirroring the ops docs example."""
+        filename = event.params["filename"]
+        event.log(f"Generating snapshot into {filename}")
+        success = self.do_snapshot(filename=filename)
+        if not success:
+            event.fail("Failed to generate snapshot.")
+            return
+        msg = f"Stored snapshot in {filename}."
+        event.set_results({"result": msg})
+
+    def do_snapshot(self, *, filename: str) -> bool:
+        """Pretend to take a snapshot of the database."""
+        del filename  # Unused in this demo stub.
+        return True
 
     def _on_demo_server_pebble_ready(self, event: ops.PebbleReadyEvent) -> None:
         """Define and start a workload using the Pebble API."""

kepler/tests/unit/test_snapshot_action.py

@@ -0,0 +1,44 @@
+# Copyright 2026 Canonical Ltd.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# To learn more about testing, see https://documentation.ubuntu.com/ops/latest/explanation/testing/
+
+"""Tests validating the ops 'manage actions' unit-test example.
+
+The docs (https://canonical.com/juju/docs/ops/latest/howto/manage-actions/#write-unit-tests)
+show a snapshot action handler that calls ``event.set_results({'result': msg})``
+and then a unit test that asserts ``'snapshot-size' in ctx.action_results``.
+
+The handler only ever sets a ``result`` key, so ``snapshot-size`` cannot be
+present in the results. This test asserts that understanding: if it passes, the
+documented assertion would fail and the doc example is incorrect.
+"""
+
+from ops import testing
+
+from charm import KosmosCharm
+
+
+def test_snapshot_action_does_not_set_snapshot_size():
+    """The snapshot action sets 'result', not 'snapshot-size'."""
+    ctx = testing.Context(KosmosCharm)
+    ctx.run(
+        ctx.on.action("snapshot", params={"filename": "db-snapshot.tar.gz"}),
+        testing.State(),
+    )
+    # The doc's handler sets results to {'result': msg}, so 'snapshot-size'
+    # is absent. The documented assertion ``'snapshot-size' in
+    # ctx.action_results`` would therefore fail.
+    assert "snapshot-size" not in ctx.action_results
+    assert ctx.action_results == {"result": "Stored snapshot in db-snapshot.tar.gz."}