Add Pico UART client and tests

tests/test_pico_core.py

@@ -78,3 +78,75 @@ def test_screen_manager():
 
     screens.previous_screen()
     assert screens.current_screen == "battery"
+
+
+class FakeUart:
+    def __init__(self):
+        self.writes = []
+        self.read_chunks = []
+
+    def write(self, data):
+        self.writes.append(data)
+
+    def any(self):
+        return len(self.read_chunks) > 0
+
+    def read(self):
+        if self.read_chunks:
+            return self.read_chunks.pop(0)
+        return b""
+
+
+def test_uart_client_send_message():
+    from comms.uart_client import UartClient
+
+    fake = FakeUart()
+    client = UartClient(fake)
+
+    client.send_message({"type": "status_request"})
+
+    assert fake.writes == [b'{"type":"status_request"}\n']
+
+
+def test_uart_client_reads_newline_delimited_json():
+    from comms.uart_client import UartClient
+
+    fake = FakeUart()
+    fake.read_chunks = [
+        b'{"type":"status_response","timestamp":1}\n',
+        b'{"type":"relay_response","relay":"fridge","enabled":true}\n',
+    ]
+
+    client = UartClient(fake)
+    messages = client.read_available_messages()
+
+    assert messages == [
+        {"type": "status_response", "timestamp": 1},
+        {"type": "relay_response", "relay": "fridge", "enabled": True},
+    ]
+
+
+def test_uart_client_handles_partial_messages():
+    from comms.uart_client import UartClient
+
+    fake = FakeUart()
+    client = UartClient(fake)
+
+    fake.read_chunks = [b'{"type":"status_', b'response"}\n']
+
+    messages = client.read_available_messages()
+
+    assert messages == [{"type": "status_response"}]
+
+
+def test_uart_client_handles_invalid_json():
+    from comms.uart_client import UartClient
+
+    fake = FakeUart()
+    fake.read_chunks = [b'not json\n']
+
+    client = UartClient(fake)
+    messages = client.read_available_messages()
+
+    assert messages[0]["type"] == "error"
+    assert messages[0]["message"] == "invalid_json"