feat: offset + CTCSS tone BCD codecs (provisional encodings)

test_civ.py

@@ -73,5 +73,36 @@ class TestParseFrames(unittest.TestCase):
         self.assertEqual(civ.parse_frames(b""), [])
 
 
+class TestOffsetCodec(unittest.TestCase):
+    # PROVISIONAL: 3-byte little-endian BCD in units of 100 Hz.
+    # Round-trip validated until pinned to a real capture (plan Task 6).
+    def test_offset_roundtrip(self):
+        for hz in (600_000, 5_000_000, 1_600_000, 0):
+            self.assertEqual(civ.bcd_to_offset(civ.offset_to_bcd(hz)), hz)
+
+    def test_offset_is_three_bytes(self):
+        self.assertEqual(len(civ.offset_to_bcd(600_000)), 3)
+
+    def test_offset_rejects_negative(self):
+        with self.assertRaises(ValueError):
+            civ.offset_to_bcd(-1)
+
+
+class TestToneCodec(unittest.TestCase):
+    # ICOM convention: CTCSS tone as 2-byte BCD of tone*10. 131.8 -> "13 18".
+    def test_tone_to_bcd_known(self):
+        self.assertEqual(civ.tone_to_bcd(88.5), b"\x08\x85")
+        self.assertEqual(civ.tone_to_bcd(131.8), b"\x13\x18")
+        self.assertEqual(civ.tone_to_bcd(100.0), b"\x10\x00")
+
+    def test_bcd_to_tone_known(self):
+        self.assertAlmostEqual(civ.bcd_to_tone(b"\x13\x18"), 131.8)
+        self.assertAlmostEqual(civ.bcd_to_tone(b"\x08\x85"), 88.5)
+
+    def test_tone_roundtrip(self):
+        for hz in (67.0, 88.5, 131.8, 146.2, 203.5):
+            self.assertAlmostEqual(civ.bcd_to_tone(civ.tone_to_bcd(hz)), hz)
+
+
 if __name__ == "__main__":
     unittest.main()