chore: update development dependencies and improve test coverage

- Upgraded `pytest-asyncio` to version 1.0 to ensure compatibility with the latest features and improvements.
- Increased the coverage threshold in pytest configuration to 80%, enhancing the quality assurance process.
- Added a new `conftest.py` file to manage shared fixtures and improve test organization.
- Introduced multiple new test files to cover various components, ensuring comprehensive test coverage across the application.
- Updated the `.coverage` file to reflect the latest coverage metrics.

tests/test_app.py

@@ -311,3 +311,47 @@ def test_calendar_ical_200_returns_only_that_users_duties(
     assert len(duties_arg) == 1
     assert duties_arg[0][0].user_id == 1
     assert duties_arg[0][1] == "User A"
+
+
+# --- /api/calendar-events ---
+
+
+@patch("duty_teller.api.app.config.EXTERNAL_CALENDAR_ICS_URL", "")
+@patch("duty_teller.api.app.config.MINI_APP_SKIP_AUTH", True)
+def test_calendar_events_empty_url_returns_empty_list(client):
+    """When EXTERNAL_CALENDAR_ICS_URL is empty, GET /api/calendar-events returns [] without fetch."""
+    with patch("duty_teller.api.app.get_calendar_events") as mock_get:
+        r = client.get(
+            "/api/calendar-events",
+            params={"from": "2025-01-01", "to": "2025-01-31"},
+        )
+    assert r.status_code == 200
+    assert r.json() == []
+    mock_get.assert_not_called()
+
+
+@patch("duty_teller.api.app.config.EXTERNAL_CALENDAR_ICS_URL", "https://example.com/cal.ics")
+@patch("duty_teller.api.app.config.MINI_APP_SKIP_AUTH", True)
+def test_calendar_events_200_returns_list_with_date_summary(client):
+    """GET /api/calendar-events with auth and URL set returns list of {date, summary}."""
+    with patch("duty_teller.api.app.get_calendar_events") as mock_get:
+        mock_get.return_value = [
+            {"date": "2025-01-15", "summary": "Team meeting"},
+            {"date": "2025-01-20", "summary": "Review"},
+        ]
+        r = client.get(
+            "/api/calendar-events",
+            params={"from": "2025-01-01", "to": "2025-01-31"},
+        )
+    assert r.status_code == 200
+    data = r.json()
+    assert len(data) == 2
+    assert data[0]["date"] == "2025-01-15"
+    assert data[0]["summary"] == "Team meeting"
+    assert data[1]["date"] == "2025-01-20"
+    assert data[1]["summary"] == "Review"
+    mock_get.assert_called_once_with(
+        "https://example.com/cal.ics",
+        from_date="2025-01-01",
+        to_date="2025-01-31",
+    )