test: add pytest suite and gate Docker builds on it

Unit tests cover the SQL gate, broadcast codec, Hive writer layout,
and flight kinematics. CI runs pytest first; the simulator image build
runs tests in a dedicated stage before the final layer.

simulator/tests/test_writer.py

@@ -0,0 +1,67 @@
+"""Hive-partitioned Parquet writer layout."""
+
+from __future__ import annotations
+
+import time
+from pathlib import Path
+
+import duckdb
+
+from virtual_drone.flight import Pose
+from virtual_drone.sensors import imu_row
+from virtual_drone.writer import PartitionWriter, make_writers
+
+
+def test_partition_path_follows_hive_layout(tmp_path: Path) -> None:
+    ts_ns = int(time.time() * 1e9)
+    writer = PartitionWriter(tmp_path, "telemetry", "flt-01", "dr-01", "imu")
+    writer.append(imu_row(
+        Pose(ts_ns=ts_ns, x=1.0, y=2.0, z=3.0, roll=0.0, pitch=0.0, yaw=0.0, vx=0.0, vy=0.0, vz=0.0),
+        __import__("random").Random(0),
+        ts_ns,
+    ))
+    writer.seal()
+
+    files = list(tmp_path.rglob("*.parquet"))
+    assert len(files) >= 1
+    path_str = str(files[0])
+    assert "dataset=telemetry" in path_str
+    assert "flight=flt-01" in path_str
+    assert "drone=dr-01" in path_str
+    assert "sensor=imu" in path_str
+    assert "year=" in path_str and "hour=" in path_str
+
+
+def test_seal_compacts_current_blocks(tmp_path: Path) -> None:
+    writer = PartitionWriter(tmp_path, "state", "flt-02", "dr-02", None)
+    base_ts = 1_700_000_000_000_000_000
+    for i in range(3):
+        writer.append({"ts_ns": base_ts + i * 5_000_000_000, "pos_x": float(i)})
+    writer.seal()
+
+    sealed = list(tmp_path.rglob("data.parquet"))
+    assert len(sealed) == 1
+    assert not list(tmp_path.rglob("current/min_*.parquet"))
+    rows = duckdb.sql(f"SELECT count(*) FROM read_parquet('{sealed[0]}')").fetchone()[0]
+    assert rows == 3
+
+
+def test_make_writers_registers_expected_datasets(tmp_path: Path) -> None:
+    writers = make_writers(tmp_path, "flt-03", "dr-03", ["imu", "battery"])
+    assert set(writers) == {"imu", "battery", "detections", "state"}
+
+
+def test_duckdb_reads_written_partition(tmp_path: Path) -> None:
+    writers = make_writers(tmp_path, "flt-04", "dr-04", ["imu"])
+    ts_ns = int(time.time() * 1e9)
+    pose = Pose(ts_ns=ts_ns, x=0.0, y=0.0, z=0.0, roll=0.0, pitch=0.0, yaw=0.0, vx=0.0, vy=0.0, vz=0.0)
+    writers["imu"].append(imu_row(pose, __import__("random").Random(1), ts_ns))
+    for w in writers.values():
+        w.seal()
+
+    count = duckdb.sql(f"""
+        SELECT count(*) FROM read_parquet(
+            '{tmp_path}/dataset=telemetry/**/*.parquet',
+            hive_partitioning=true, union_by_name=true)
+    """).fetchone()[0]
+    assert count >= 1