diff --git a/discovery.py b/discovery.py
index c0def93..f7f0116 100644
--- a/discovery.py
+++ b/discovery.py
@@ -34,6 +34,14 @@ class Camera:
     extra_video_devices: list[str] = field(default_factory=list)
 
 
+def select_cameras(cameras: list[Camera], spec: list[str]) -> list[Camera]:
+    """`--cameras 1,5` means identities cam-01 and cam-05, not discovery index."""
+    if spec == ["all"]:
+        return list(cameras)
+    wanted = {f"cam-{int(i):02d}" for i in spec}
+    return [c for c in cameras if c.identity in wanted]
+
+
 def _run(cmd: list[str]) -> str:
     return subprocess.run(cmd, capture_output=True, text=True, check=False).stdout
 
diff --git a/pyproject.toml b/pyproject.toml
index 1dedf71..55c8b50 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -11,3 +11,6 @@ dependencies = [
     "opencv-python-headless",
     "scipy",
 ]
+
+[project.optional-dependencies]
+dev = ["pytest>=8"]
diff --git a/run.py b/run.py
index 760cd71..663ad08 100644
--- a/run.py
+++ b/run.py
@@ -21,7 +21,7 @@ import time
 from pathlib import Path
 
 from config import load_config, _load_dotenv
-from discovery import discover_cameras
+from discovery import discover_cameras, select_cameras
 from tokens import make_token
 
 log = logging.getLogger("cameras.main")
@@ -126,12 +126,10 @@ def main() -> int:
                  c.audio_card if c.audio_card is not None else "-",
                  c.usb_port or "-")
 
-    if cfg.cameras != ["all"]:
-        wanted = set(int(i) - 1 for i in cfg.cameras)
-        cameras = [c for c in cameras if c.index in wanted]
-        if not cameras:
-            log.error("no cameras match --cameras %s", args.cameras)
-            return 2
+    cameras = select_cameras(cameras, cfg.cameras)
+    if not cameras:
+        log.error("no cameras match --cameras %s", args.cameras)
+        return 2
 
     sup = Supervisor(cfg, cameras)
     for cam in cameras:
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..94bf69b
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,5 @@
+import sys
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+sys.path.insert(0, str(ROOT))
diff --git a/tests/test_audio_cleanup.py b/tests/test_audio_cleanup.py
new file mode 100644
index 0000000..a1cb746
--- /dev/null
+++ b/tests/test_audio_cleanup.py
@@ -0,0 +1,30 @@
+import inspect
+
+import numpy as np
+import pytest
+
+from audio_cleanup import AudioCleaner
+
+
+def test_enhance_batch_without_lengths_typeerror():
+    c = AudioCleaner(mode="force")
+    assert c.backend == "model"
+    import torch
+
+    w = torch.zeros(1, 8000)
+    with pytest.raises(TypeError):
+        c._enhancer.enhance_batch(w)
+
+
+def test_process_uses_relative_lengths_one():
+    src = inspect.getsource(AudioCleaner.process)
+    assert "tensor([1.0])" in src
+
+
+def test_process_preserves_length_and_int16():
+    c = AudioCleaner(mode="force")
+    n = 16000
+    pcm = (np.sin(2 * np.pi * 440 * np.arange(n) / 16000) * 8000).astype(np.int16)
+    out = c.process(pcm)
+    assert out.dtype == np.int16
+    assert out.shape == pcm.shape
diff --git a/tests/test_config.py b/tests/test_config.py
new file mode 100644
index 0000000..bff5236
--- /dev/null
+++ b/tests/test_config.py
@@ -0,0 +1,7 @@
+from config import _parse_cameras
+
+
+def test_parse_cameras_list():
+    assert _parse_cameras("1,5") == ["1", "5"]
+    assert _parse_cameras("all") == ["all"]
+    assert _parse_cameras("1-3") == ["1", "2", "3"]
diff --git a/tests/test_discovery.py b/tests/test_discovery.py
new file mode 100644
index 0000000..76f6898
--- /dev/null
+++ b/tests/test_discovery.py
@@ -0,0 +1,49 @@
+import re
+
+from discovery import Camera, discover_cameras, select_cameras
+
+CARD_RE = re.compile(r"\s*(\d+)\s+\[([A-Za-z0-9_]+)\s*\]:\s*(.*)")
+
+
+def test_padded_c920_card_line_matches():
+    line = " 2 [C920            ]: USB-Audio - HD Pro Webcam C920"
+    m = CARD_RE.match(line)
+    assert m is not None
+    assert int(m.group(1)) == 2
+    assert m.group(2) == "C920"
+
+
+def test_naive_word_regex_misses_padding():
+    line = " 2 [C920            ]: USB-Audio - HD Pro Webcam C920"
+    assert re.match(r"\s*(\d+)\s+\[(\w+)\]:", line) is None
+
+
+def test_live_discover_present_cameras():
+    cams = discover_cameras()
+    assert len(cams) >= 1
+    assert all(c.audio_card is not None for c in cams)
+    assert all(c.serial for c in cams)
+    assert all(re.match(r"cam-\d{2}$", c.identity) for c in cams)
+    ids = [c.identity for c in cams]
+    assert ids == sorted(ids)
+
+
+def test_select_cameras_by_identity_not_index():
+    cams = [
+        Camera(index=0, identity="cam-01", video_device="/dev/cam01",
+               audio_card=2, serial="A"),
+        Camera(index=1, identity="cam-05", video_device="/dev/cam05",
+               audio_card=6, serial="B"),
+        Camera(index=2, identity="cam-20", video_device="/dev/cam20",
+               audio_card=21, serial="C"),
+    ]
+    out = select_cameras(cams, ["1", "5"])
+    assert [c.identity for c in out] == ["cam-01", "cam-05"]
+
+
+def test_select_cameras_all():
+    cams = [
+        Camera(index=0, identity="cam-01", video_device="/dev/cam01",
+               audio_card=2, serial="A"),
+    ]
+    assert select_cameras(cams, ["all"]) == cams