hil: make the usbtest-cell tests actually run

The file was bare module-level pytest functions with no entry point, and nothing
in this repo invokes pytest - so `python3 test_hil_usbtest_cell.py` exited 0
having run nothing, and the guard on the skip-accounting fix could never fail.
Converted to unittest with a __main__ block, matching its two siblings.

A pre-commit hook now runs every test/hil/test_*.py directly. Not via pytest:
hil_test.py matches pytest's default discovery glob, so `pytest test/hil/`
collects 26 hardware cases and errors on all of them. Verified the hook gates -
reintroducing the passed+failed total makes it exit non-zero.

.pre-commit-config.yaml

@@ -48,6 +48,16 @@ repos:
     types_or: [c, header]
     language: system
 
+  # The HIL harness's hardware-free unit tests. Each is run directly rather than through pytest:
+  # nothing else in the repo invokes pytest, and `pytest test/hil/` would collect hil_test.py's
+  # hardware cases (they match pytest's default glob) and error on every one.
+  - id: hil-unit-test
+    name: HIL harness unit tests
+    files: ^test/hil/
+    entry: sh -c 'for t in test/hil/test_*.py; do python3 "$t" || exit 1; done'
+    pass_filenames: false
+    language: system
+
 #  - id: build-fuzzer
 #    name: build-fuzzer
 #    files: ^(src/|test/fuzz/)

test/hil/test_hil_usbtest_cell.py

@@ -1,38 +1,45 @@
-"""The usbtest report cell must never render a quirk-skipped run as a full pass."""
+#!/usr/bin/env python3
+"""The usbtest report cell must never render a quirk-skipped run as a full pass.
+
+unittest (not bare pytest functions) so `python3 test_hil_usbtest_cell.py` actually runs the
+assertions: nothing in CI invokes pytest, and `pytest test/hil/` is not a substitute either -
+hil_test.py matches pytest's default discovery glob and drags 26 hardware tests into collection.
+"""
 import sys
+import unittest
 from pathlib import Path
 
 sys.path.insert(0, str(Path(__file__).resolve().parent))
 import hil_test
 
 
-def test_full_pass_renders_as_pass():
-    data = {'passed': 30, 'failed': 0, 'skipped': 0, 'cases': []}
-    assert hil_test.usbtest_cell(data) == '✅ 30/30'
+class TestUsbtestCell(unittest.TestCase):
+    def test_full_pass_renders_as_pass(self):
+        data = {'passed': 30, 'failed': 0, 'skipped': 0, 'cases': []}
+        self.assertEqual(hil_test.usbtest_cell(data), '✅ 30/30')
+
+    def test_skipped_cases_are_counted_in_the_denominator(self):
+        """25 ran and passed, 5 were quirk-skipped: the cell must not read 25/25."""
+        data = {'passed': 25, 'failed': 0, 'skipped': 5,
+                'cases': [{'num': n, 'status': 'SKIP'} for n in (9, 10, 13, 14, 21)]}
+        cell = hil_test.usbtest_cell(data)
+        self.assertIn('25/30', cell)
+        self.assertIn('5 skipped', cell)
+        self.assertNotIn('25/25', cell)
+
+    def test_skipped_cases_are_not_reported_as_failures(self):
+        data = {'passed': 24, 'failed': 1, 'skipped': 5,
+                'cases': [{'num': n, 'status': 'SKIP'} for n in (9, 10, 13, 14, 21)]
+                         + [{'num': 7, 'status': 'FAIL'}]}
+        with self.assertRaises(hil_test.TestFail) as cm:
+            hil_test.usbtest_cell(data)
+        self.assertIn('cases failed: [7]', str(cm.exception))
+
+    def test_missing_skipped_key_defaults_to_zero(self):
+        """Output from a usbtest.py predating the skipped key must still render."""
+        self.assertEqual(hil_test.usbtest_cell({'passed': 30, 'failed': 0, 'cases': []}),
+                         '✅ 30/30')
 
 
-def test_skipped_cases_are_counted_in_the_denominator():
-    # 25 ran and passed, 5 were quirk-skipped: the cell must not read 25/25
-    data = {'passed': 25, 'failed': 0, 'skipped': 5,
-            'cases': [{'num': n, 'status': 'SKIP'} for n in (9, 10, 13, 14, 21)]}
-    cell = hil_test.usbtest_cell(data)
-    assert '25/30' in cell
-    assert '5 skipped' in cell
-    assert '25/25' not in cell
-
-
-def test_skipped_cases_are_not_reported_as_failures():
-    data = {'passed': 24, 'failed': 1, 'skipped': 5,
-            'cases': [{'num': n, 'status': 'SKIP'} for n in (9, 10, 13, 14, 21)]
-                     + [{'num': 7, 'status': 'FAIL'}]}
-    try:
-        hil_test.usbtest_cell(data)
-    except hil_test.TestFail as e:
-        assert 'cases failed: [7]' in str(e)
-    else:
-        raise AssertionError('expected TestFail')
-
-
-def test_missing_skipped_key_defaults_to_zero():
-    # older usbtest.py output without the key must still render
-    assert hil_test.usbtest_cell({'passed': 30, 'failed': 0, 'cases': []}) == '✅ 30/30'
+if __name__ == '__main__':
+    unittest.main(verbosity=1)