Improve Location docs and tests (#29)

- **Improve `Location.timezone` documentation**
- **Add tests for the `Location.timezone` lookup**

src/frequenz/client/microgrid/_metadata.py

@@ -24,8 +24,10 @@ class Location:
     timezone: ZoneInfo | None = None
     """The timezone of the microgrid.
 
-    The timezone will be set to None if the latitude or longitude points
-    are not set or the timezone cannot be found given the location points.
+    If not passed during construction (or `None` is passed), and there is a `longitude`
+    and `latitude`, then the timezone wil be looked up in a database based on the
+    coordinates. This lookup could fail, in which case the timezone will still be
+    `None`.
     """
 
     def __post_init__(self) -> None:

tests/test_metadata.py

@@ -0,0 +1,67 @@
+# License: MIT
+# Copyright © 2024 Frequenz Energy-as-a-Service GmbH
+
+"""Tests for the microgrid metadata types."""
+
+from typing import Iterator
+from unittest.mock import MagicMock, patch
+from zoneinfo import ZoneInfo
+
+import pytest
+
+from frequenz.client.microgrid import Location
+
+
+@pytest.fixture
+def timezone_finder() -> Iterator[MagicMock]:
+    """Return a mock timezone finder."""
+    with patch(
+        "frequenz.client.microgrid._metadata._timezone_finder", autospec=True
+    ) as mock_timezone_finder:
+        yield mock_timezone_finder
+
+
+@pytest.mark.parametrize(
+    "latitude, longitude, timezone",
+    [
+        (None, None, None),
+        (52.52, None, None),
+        (None, 13.405, None),
+        (None, None, ZoneInfo(key="UTC")),
+        (52.52, None, ZoneInfo(key="UTC")),
+        (None, 13.405, ZoneInfo(key="UTC")),
+        (52.52, 13.405, ZoneInfo(key="UTC")),
+    ],
+    ids=str,
+)
+def test_location_timezone_not_looked_up_if_not_possible_or_necessary(
+    timezone_finder: MagicMock,
+    latitude: float | None,
+    longitude: float | None,
+    timezone: ZoneInfo | None,
+) -> None:
+    """Test the location timezone is not looked up if is not necessary or possible."""
+    timezone_finder.timezone_at.return_value = "Europe/Berlin"
+
+    location = Location(latitude=latitude, longitude=longitude, timezone=timezone)
+
+    assert location.latitude == latitude
+    assert location.longitude == longitude
+    assert location.timezone == timezone
+    timezone_finder.timezone_at.assert_not_called()
+
+
+@pytest.mark.parametrize("timezone", [None, "Europe/Berlin"], ids=str)
+def test_location_timezone_lookup(
+    timezone_finder: MagicMock, timezone: str | None
+) -> None:
+    """Test the location timezone is looked up if not provided and there is enough info."""
+    timezone_finder.timezone_at.return_value = timezone
+
+    location = Location(latitude=52.52, longitude=13.405)
+
+    if timezone is None:
+        assert location.timezone is None
+    else:
+        assert location.timezone == ZoneInfo(key=timezone)
+    timezone_finder.timezone_at.assert_called_once_with(lat=52.52, lng=13.405)