Another iteration based on feedback from hardware synth testing.

tests/unit/test_hardware_speech_drivers.py

@@ -146,6 +146,28 @@ def test_auto_device_detection_fails_when_no_serial_device(monkeypatch):
     )
 
 
+def test_hardware_driver_retries_partial_serial_writes(monkeypatch):
+    speech_driver = litetalkDriver.driver()
+    speech_driver.env = build_environment("/dev/ttyUSB0")
+    speech_driver.serial_port = 12
+    written_chunks = []
+
+    def fake_write(port, data):
+        assert port == 12
+        chunk = data[:2]
+        written_chunks.append(chunk)
+        return len(chunk)
+
+    monkeypatch.setattr(
+        "fenrirscreenreader.speechDriver.hardwareSerialDriver.os.write",
+        fake_write,
+    )
+
+    speech_driver._write_bytes(b"abcdef", "speech")
+
+    assert written_chunks == [b"ab", b"cd", b"ef"]
+
+
 @pytest.mark.parametrize("driver_class", [doubletalkDriver, tripletalkDriver])
 def test_litetalk_compatible_alias_drivers(driver_class, serial_pair):
     speech_driver, master_fd = initialized_driver(driver_class, serial_pair)