from frame_shm import LatestFrameReader, LatestFrameWriter, frame_bytes


def test_latest_frame_roundtrip(tmp_path):
    path = str(tmp_path / "cam-01.i420")
    w, h = 16, 16
    n = frame_bytes(w, h)
    writer = LatestFrameWriter(path, w, h)
    payload = bytes(range(256)) * (n // 256 + 1)
    payload = payload[:n]
    seq = writer.write(payload)
    assert seq == 1
    reader = LatestFrameReader(path)
    got = reader.latest()
    assert got is not None
    assert got[0] == 1
    assert got[1] == payload
    seq2 = writer.write(bytes([3]) * n)
    got2 = reader.latest()
    assert got2 is not None
    assert got2[0] == seq2
    assert got2[1][0] == 3
    writer.close()