Add unit tests for custom charm functionality

charm/tests/unit/test_charm.py

@@ -0,0 +1,105 @@
+# Copyright 2026 Canonical Ltd.
+# See LICENSE file for licensing details.
+
+"""Unit tests for the dashboard charm's custom functionality.
+
+Tests cover: load-sample-data action (the only custom code on top of django-framework).
+"""
+
+import os
+import pathlib
+import sys
+import unittest.mock
+
+import ops
+import pytest
+
+mock_paas = unittest.mock.MagicMock()
+mock_paas.django.Charm = ops.CharmBase
+sys.modules["paas_charm"] = mock_paas
+sys.modules["paas_charm.django"] = mock_paas.django
+
+CHARM_DIR = pathlib.Path(__file__).parents[2]
+sys.path.insert(0, str(CHARM_DIR / "src"))
+
+os.environ["SCENARIO_SKIP_CONSISTENCY_CHECKS"] = "1"
+
+import charm  # noqa: E402
+import ops.testing  # noqa: E402
+
+
+def _patch_parent(mgr):
+    container_obj = mgr.charm.unit.get_container("django-app")
+    mgr.charm._container = container_obj
+    mgr.charm._workload_config = unittest.mock.MagicMock()
+    mgr.charm._workload_config.app_dir = pathlib.PurePosixPath("/srv/app")
+    return container_obj
+
+
+class TestLoadSampleDataAction:
+    """Test the load-sample-data action."""
+
+    def test_load_sample_data_runs_loaddata(self):
+        """load-sample-data executes Django loaddata command."""
+        ctx = ops.testing.Context(charm.DashboardCharm, charm_root=CHARM_DIR)
+        container = ops.testing.Container("django-app", can_connect=True)
+        state = ops.testing.State(containers={container}, leader=True)
+
+        with ctx(ctx.on.action("load-sample-data"), state) as mgr:
+            container_obj = _patch_parent(mgr)
+            mock_process = unittest.mock.MagicMock()
+            mock_process.wait.return_value = None
+            container_obj.exec = unittest.mock.MagicMock(return_value=mock_process)
+            mgr.run()
+
+            container_obj.exec.assert_called_once()
+            call_args = container_obj.exec.call_args
+            assert call_args[0][0] == [
+                "python3", "manage.py", "loaddata", "initial_data.yaml"
+            ]
+            assert call_args[1]["working_dir"] == "/srv/app"
+            assert call_args[1]["service_context"] == "django"
+
+        assert ctx.action_results == {"result": "loaded sample data"}
+
+    def test_load_sample_data_fails_on_exec_error(self):
+        """load-sample-data action fails when exec raises an error."""
+        ctx = ops.testing.Context(charm.DashboardCharm, charm_root=CHARM_DIR)
+        container = ops.testing.Container("django-app", can_connect=True)
+        state = ops.testing.State(containers={container}, leader=True)
+
+        with pytest.raises(ops.testing.ActionFailed) as exc_info:
+            with ctx(ctx.on.action("load-sample-data"), state) as mgr:
+                container_obj = _patch_parent(mgr)
+                container_obj.exec = unittest.mock.MagicMock(
+                    side_effect=ops.pebble.APIError(
+                        body={},
+                        code=500,
+                        status="Internal Server Error",
+                        message="container not ready",
+                    )
+                )
+                mgr.run()
+
+        assert "unable to load sample data" in exc_info.value.message
+
+    def test_load_sample_data_fails_on_change_error(self):
+        """load-sample-data fails when process.wait() raises ChangeError."""
+        ctx = ops.testing.Context(charm.DashboardCharm, charm_root=CHARM_DIR)
+        container = ops.testing.Container("django-app", can_connect=True)
+        state = ops.testing.State(containers={container}, leader=True)
+
+        with pytest.raises(ops.testing.ActionFailed) as exc_info:
+            with ctx(ctx.on.action("load-sample-data"), state) as mgr:
+                container_obj = _patch_parent(mgr)
+                mock_process = unittest.mock.MagicMock()
+                mock_process.wait.side_effect = ops.pebble.ChangeError(
+                    err="command failed",
+                    change=unittest.mock.MagicMock(),
+                )
+                container_obj.exec = unittest.mock.MagicMock(
+                    return_value=mock_process
+                )
+                mgr.run()
+
+        assert "unable to load sample data" in exc_info.value.message