Implement story 2.1: aircraft data model and fetcher

Add HttpFetcher and FileFixtureFetcher with shared _parse_aircraft helper,
DUMP1090_URL constant, realistic fixture data, and full test coverage for
all acceptance criteria (AC1–AC5).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_fetcher.py

@@ -1,2 +1,124 @@
-def test_placeholder() -> None:
-    pass
+from pathlib import Path
+from unittest.mock import MagicMock, patch
+
+import pytest
+import requests
+
+from planemapper.fetcher import FileFixtureFetcher, HttpFetcher
+
+_FIXTURES = Path(__file__).parent / "fixtures" / "aircraft_sample.json"
+
+_FULL_RESPONSE = {
+    "aircraft": [
+        {
+            "hex": "4ca7f2",
+            "lat": 53.3498,
+            "lon": -6.2603,
+            "flight": "EIN123  ",
+            "altitude": 12000,
+            "category": "A3",
+            "track": 270.0,
+            "mlat": [],
+        }
+    ]
+}
+
+_DEFAULTS_RESPONSE = {
+    "aircraft": [
+        {
+            "hex": "aabbcc",
+            "lat": 51.0,
+            "lon": -1.0,
+        }
+    ]
+}
+
+_MLAT_RESPONSE = {
+    "aircraft": [
+        {
+            "hex": "dddddd",
+            "lat": 52.0,
+            "lon": -2.0,
+            "mlat": ["lat", "lon"],
+        }
+    ]
+}
+
+
+def _mock_get(payload: dict) -> MagicMock:
+    mock_resp = MagicMock()
+    mock_resp.json.return_value = payload
+    mock_resp.raise_for_status = MagicMock()
+    return mock_resp
+
+
+def test_http_fetcher_full_response() -> None:
+    with patch("planemapper.fetcher.requests.get", return_value=_mock_get(_FULL_RESPONSE)):
+        aircraft = HttpFetcher().fetch()
+    assert len(aircraft) == 1
+    a = aircraft[0]
+    assert a.icao == "4ca7f2"
+    assert a.lat == 53.3498
+    assert a.lon == -6.2603
+    assert a.callsign == "EIN123"
+    assert a.altitude_ft == 12000
+    assert a.category == "A3"
+    assert a.heading == 270.0
+    assert a.is_mlat is False
+    assert a.is_stale is False
+
+
+def test_http_fetcher_missing_fields_use_defaults() -> None:
+    with patch("planemapper.fetcher.requests.get", return_value=_mock_get(_DEFAULTS_RESPONSE)):
+        aircraft = HttpFetcher().fetch()
+    assert len(aircraft) == 1
+    a = aircraft[0]
+    assert a.callsign == ""
+    assert a.altitude_ft == 0
+    assert a.category == ""
+    assert a.is_mlat is False
+
+
+def test_http_fetcher_altitude_ground_string() -> None:
+    payload = {"aircraft": [{"hex": "aaa", "lat": 51.0, "lon": -1.0, "altitude": "ground"}]}
+    with patch("planemapper.fetcher.requests.get", return_value=_mock_get(payload)):
+        aircraft = HttpFetcher().fetch()
+    assert aircraft[0].altitude_ft == 0
+
+
+def test_http_fetcher_skips_entries_without_position() -> None:
+    payload = {"aircraft": [{"hex": "nopos"}, {"hex": "haspos", "lat": 51.0, "lon": -1.0}]}
+    with patch("planemapper.fetcher.requests.get", return_value=_mock_get(payload)):
+        aircraft = HttpFetcher().fetch()
+    assert len(aircraft) == 1
+    assert aircraft[0].icao == "haspos"
+
+
+def test_http_fetcher_propagates_timeout() -> None:
+    with patch("planemapper.fetcher.requests.get", side_effect=requests.Timeout):
+        with pytest.raises(requests.Timeout):
+            HttpFetcher().fetch()
+
+
+def test_http_fetcher_mlat_flag() -> None:
+    with patch("planemapper.fetcher.requests.get", return_value=_mock_get(_MLAT_RESPONSE)):
+        aircraft = HttpFetcher().fetch()
+    assert aircraft[0].is_mlat is True
+
+
+def test_file_fixture_fetcher_returns_aircraft() -> None:
+    aircraft = FileFixtureFetcher(_FIXTURES).fetch()
+    assert len(aircraft) == 4
+
+
+def test_file_fixture_fetcher_no_network_call() -> None:
+    with patch("planemapper.fetcher.requests.get") as mock_get:
+        FileFixtureFetcher(_FIXTURES).fetch()
+    mock_get.assert_not_called()
+
+
+def test_file_fixture_fetcher_mlat_aircraft() -> None:
+    aircraft = FileFixtureFetcher(_FIXTURES).fetch()
+    mlat_aircraft = [a for a in aircraft if a.is_mlat]
+    assert len(mlat_aircraft) == 1
+    assert mlat_aircraft[0].icao == "4003c3"