fix(tests): skip ffmpeg-dependent tests when binary is missing

The CI runner doesn't have ffmpeg installed. Tests that generate
silent audio or compose video+audio are now marked requires_ffmpeg
and skipped gracefully in that environment.

Made-with: Cursor

Author: jmjava

tests/test_validate.py

@@ -6,6 +6,7 @@
 
 from __future__ import annotations
 
+import shutil
 import subprocess
 from pathlib import Path
 
@@ -18,6 +19,9 @@
 from docgen.config import Config
 from docgen.validate import Validator, _sample_frames
 
+_has_ffmpeg = shutil.which("ffmpeg") is not None
+requires_ffmpeg = pytest.mark.skipif(not _has_ffmpeg, reason="ffmpeg not installed")
+
 
 # ── Helpers: create synthetic test videos ─────────────────────────────
 
@@ -252,6 +256,7 @@ def test_check_freeze_ratio_math(self, config):
         assert c.check_freeze_ratio(100.0, 0.0) == pytest.approx(1.0)
         assert c.check_freeze_ratio(0.0, 50.0) == pytest.approx(0.0)
 
+    @requires_ffmpeg
     def test_compose_rejects_short_video(self, config, cfg_dir):
         """Compose in strict mode should raise when video is way shorter than audio."""
         audio = cfg_dir / "audio" / "01-test.mp3"
@@ -264,6 +269,7 @@ def test_compose_rejects_short_video(self, config, cfg_dir):
         with pytest.raises(ComposeError, match="FREEZE GUARD"):
             c._compose_simple("01", video, strict=True)
 
+    @requires_ffmpeg
     def test_compose_allows_matching_durations(self, config, cfg_dir):
         """Compose should succeed when video roughly matches audio."""
         audio = cfg_dir / "audio" / "01-test.mp3"
@@ -276,6 +282,7 @@ def test_compose_allows_matching_durations(self, config, cfg_dir):
         result = c._compose_simple("01", video, strict=True)
         assert result is True
 
+    @requires_ffmpeg
     def test_compose_nonstrict_warns(self, config, cfg_dir, capsys):
         """Non-strict mode prints a warning but doesn't raise."""
         audio = cfg_dir / "audio" / "01-test.mp3"
@@ -329,6 +336,7 @@ def test_half_black_fails_pre_push(self, config, cfg_dir):
         with pytest.raises(SystemExit):
             v.run_pre_push()
 
+    @requires_ffmpeg
     def test_static_video_does_not_fail_pre_push(self, config, cfg_dir):
         """freeze_ratio is a soft check — static (non-black) video only warns."""
         vid = cfg_dir / "recordings" / "01-test.mp4"