Add video SynthID experiment harness

tests/test_video_synthid_sweep.py

@@ -0,0 +1,67 @@
+"""Pure regression tests for the oracle-gated video SynthID experiment."""
+
+from __future__ import annotations
+
+import importlib.util
+from pathlib import Path
+from typing import TYPE_CHECKING
+
+import numpy as np
+import pytest
+import torch
+
+if TYPE_CHECKING:
+    from types import ModuleType
+
+_SCRIPT = Path(__file__).parent.parent / "scripts" / "video_synthid_sweep.py"
+
+
+@pytest.fixture(scope="module")
+def sweep() -> ModuleType:
+    spec = importlib.util.spec_from_file_location("video_synthid_sweep", _SCRIPT)
+    assert spec is not None
+    assert spec.loader is not None
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
+def test_fit_size_preserves_landscape_aspect_and_vae_alignment(sweep: ModuleType) -> None:
+    assert sweep._fit_size(1280, 720, 512) == (512, 288)
+
+
+def test_fit_size_rejects_invalid_dimensions(sweep: ModuleType) -> None:
+    with pytest.raises(ValueError, match="positive"):
+        sweep._fit_size(0, 720, 512)
+
+
+def test_shared_latent_noise_is_one_spatial_field(sweep: ModuleType) -> None:
+    noise = sweep._shared_latent_noise(
+        (4, 8, 8),
+        seed=7,
+        device="cpu",
+        dtype=torch.float32,
+    )
+    assert noise.shape == (1, 4, 8, 8)
+
+
+def test_shared_latent_noise_is_seeded(sweep: ModuleType) -> None:
+    first = sweep._shared_latent_noise((4, 8, 8), seed=7, device="cpu", dtype=torch.float32)
+    repeated = sweep._shared_latent_noise((4, 8, 8), seed=7, device="cpu", dtype=torch.float32)
+    other = sweep._shared_latent_noise((4, 8, 8), seed=8, device="cpu", dtype=torch.float32)
+    assert torch.equal(first, repeated)
+    assert not torch.equal(first, other)
+
+
+def test_psnr_is_infinite_for_identical_frames(sweep: ModuleType) -> None:
+    frame = np.full((2, 8, 8, 3), 120, dtype=np.uint8)
+    assert sweep._psnr(frame, frame.copy()) == pytest.approx(float("inf"))
+
+
+def test_temporal_residual_ratio_is_one_for_identical_sequences(sweep: ModuleType) -> None:
+    first = np.zeros((32, 32, 3), dtype=np.uint8)
+    second = first.copy()
+    second[:, 8:16] = 80
+    sequence = [first, second]
+    maps, baseline = sweep._temporal_reference(sequence)
+    assert sweep._temporal_residual_ratio([frame.copy() for frame in sequence], maps, baseline) == pytest.approx(1.0)