Lin_Simulator/python/tests/test_connection.py

"""
test_connection.py — Tests for Step 5: Connection panel & device discovery.

Tests the ConnectionManager state machine and the GUI integration.
Uses mocking since we don't have real BabyLIN hardware in tests.

MOCKING IN TESTS:
=================
    "Mocking" means replacing a real object with a fake one that
    behaves predictably. We mock:
      - serial.tools.list_ports.comports() → return fake port list
      - serial.Serial() → return a fake serial port object
    This lets us test the connect/disconnect logic without hardware.

    Python's unittest.mock provides:
      - patch(): temporarily replace a function/class during a test
      - MagicMock(): create a fake object that records all calls to it

    # In C/C++, you'd achieve this with dependency injection or
    # link-time substitution (replacing a .o file with a mock .o).
"""

import sys
import pytest
from pathlib import Path
from unittest.mock import patch, MagicMock

sys.path.insert(0, str(Path(__file__).parent.parent / "src"))

from PyQt6.QtWidgets import QApplication
from connection_manager import ConnectionManager, ConnectionState, PortInfo

SAMPLE_LDF = str(Path(__file__).parent.parent.parent / "resources" / "sample.ldf")


@pytest.fixture(scope="session")
def app():
    application = QApplication.instance() or QApplication(sys.argv)
    yield application


@pytest.fixture
def mgr():
    """Fresh ConnectionManager for each test."""
    return ConnectionManager()


@pytest.fixture
def window(app):
    from main_window import MainWindow
    w = MainWindow()
    w._load_ldf_file(SAMPLE_LDF)
    return w


# ─── ConnectionManager Unit Tests ─────────────────────────────────────

class TestConnectionState:
    """Test the connection state machine."""

    def test_initial_state_disconnected(self, mgr):
        assert mgr.state == ConnectionState.DISCONNECTED

    def test_not_connected_initially(self, mgr):
        assert not mgr.is_connected

    def test_no_error_initially(self, mgr):
        assert mgr.error_message == ""

    def test_no_port_initially(self, mgr):
        assert mgr.connected_port is None


class TestPortScanning:
    """Test serial port enumeration."""

    @patch("connection_manager.serial.tools.list_ports.comports")
    def test_scan_returns_ports(self, mock_comports, mgr):
        """Mock comports() to return fake ports."""
        # Create fake port objects that have .device, .description, .hwid
        fake_port = MagicMock()
        fake_port.device = "/dev/ttyUSB0"
        fake_port.description = "BabyLIN USB"
        fake_port.hwid = "USB VID:PID=1234:5678"
        mock_comports.return_value = [fake_port]

        ports = mgr.scan_ports()
        assert len(ports) == 1
        assert ports[0].device == "/dev/ttyUSB0"
        assert ports[0].description == "BabyLIN USB"

    @patch("connection_manager.serial.tools.list_ports.comports")
    def test_scan_empty_when_no_devices(self, mock_comports, mgr):
        mock_comports.return_value = []
        ports = mgr.scan_ports()
        assert len(ports) == 0


class TestConnect:
    """Test connect/disconnect flow."""

    @patch("connection_manager.serial.Serial")
    def test_connect_success(self, mock_serial_class, mgr):
        """Mock Serial() to simulate successful connection."""
        mock_serial_class.return_value = MagicMock()

        result = mgr.connect("/dev/ttyUSB0", 19200)
        assert result is True
        assert mgr.state == ConnectionState.CONNECTED
        assert mgr.is_connected
        assert mgr.connected_port is not None
        assert mgr.connected_port.device == "/dev/ttyUSB0"

    @patch("connection_manager.serial.Serial")
    def test_connect_failure(self, mock_serial_class, mgr):
        """Mock Serial() to simulate connection failure."""
        import serial
        mock_serial_class.side_effect = serial.SerialException("Port not found")

        result = mgr.connect("/dev/nonexistent", 19200)
        assert result is False
        assert mgr.state == ConnectionState.ERROR
        assert "Port not found" in mgr.error_message

    @patch("connection_manager.serial.Serial")
    def test_disconnect_after_connect(self, mock_serial_class, mgr):
        mock_serial_instance = MagicMock()
        mock_serial_instance.is_open = True
        mock_serial_class.return_value = mock_serial_instance

        mgr.connect("/dev/ttyUSB0")
        mgr.disconnect()

        assert mgr.state == ConnectionState.DISCONNECTED
        assert not mgr.is_connected
        assert mgr.connected_port is None
        # Verify serial.close() was called
        mock_serial_instance.close.assert_called_once()

    def test_disconnect_when_already_disconnected(self, mgr):
        """Disconnecting when already disconnected should be a no-op."""
        mgr.disconnect()
        assert mgr.state == ConnectionState.DISCONNECTED

    @patch("connection_manager.serial.Serial")
    def test_reconnect_disconnects_first(self, mock_serial_class, mgr):
        """Connecting when already connected should disconnect first."""
        mock_serial_instance = MagicMock()
        mock_serial_instance.is_open = True
        mock_serial_class.return_value = mock_serial_instance

        mgr.connect("/dev/ttyUSB0")
        mgr.connect("/dev/ttyUSB1")

        # First connection should have been closed
        mock_serial_instance.close.assert_called()


# ─── GUI Integration Tests ────────────────────────────────────────────

class TestConnectionUI:
    """Test that connection state changes update the GUI correctly."""

    def test_initial_ui_disconnected(self, window):
        assert "Disconnected" in window.lbl_conn_status.text()
        assert window.btn_connect.isEnabled()
        assert not window.btn_disconnect.isEnabled()

    @patch("connection_manager.serial.Serial")
    def test_ui_after_connect(self, mock_serial_class, window):
        mock_serial_class.return_value = MagicMock()

        # Add a fake device to the dropdown
        window.combo_device.addItem("Test Port", "/dev/ttyUSB0")
        window.combo_device.setCurrentIndex(0)
        window._on_connect()

        assert "Connected" in window.lbl_conn_status.text()
        assert not window.btn_connect.isEnabled()
        assert window.btn_disconnect.isEnabled()
        assert "Connected" in window.lbl_status_connection.text()

    @patch("connection_manager.serial.Serial")
    def test_ui_after_disconnect(self, mock_serial_class, window):
        mock_instance = MagicMock()
        mock_instance.is_open = True
        mock_serial_class.return_value = mock_instance

        window.combo_device.addItem("Test Port", "/dev/ttyUSB0")
        window.combo_device.setCurrentIndex(0)
        window._on_connect()
        window._on_disconnect()

        assert "Disconnected" in window.lbl_conn_status.text()
        assert window.btn_connect.isEnabled()
        assert not window.btn_disconnect.isEnabled()

    @patch("connection_manager.serial.Serial")
    def test_ui_after_error(self, mock_serial_class, window):
        import serial
        mock_serial_class.side_effect = serial.SerialException("Access denied")

        window.combo_device.addItem("Test Port", "/dev/ttyUSB0")
        window.combo_device.setCurrentIndex(0)

        # Monkeypatch the error dialog to avoid blocking
        with patch.object(type(window), '_on_connect', lambda self: (
            self._conn_mgr.connect(self.combo_device.currentData()),
            self._update_connection_ui()
        )):
            window._conn_mgr.connect("/dev/ttyUSB0")
            window._update_connection_ui()

        assert "Error" in window.lbl_conn_status.text()
        assert window.btn_connect.isEnabled()  # Can retry

    @patch("connection_manager.serial.tools.list_ports.comports")
    def test_refresh_populates_dropdown(self, mock_comports, window):
        fake_port = MagicMock()
        fake_port.device = "/dev/ttyUSB0"
        fake_port.description = "BabyLIN USB"
        fake_port.hwid = "USB VID:PID=1234:5678"
        mock_comports.return_value = [fake_port]

        window._on_refresh_devices()

        assert window.combo_device.count() == 1
        assert "/dev/ttyUSB0" in window.combo_device.itemText(0)

    @patch("connection_manager.serial.tools.list_ports.comports")
    def test_refresh_empty_when_no_devices(self, mock_comports, window):
        mock_comports.return_value = []
        window._on_refresh_devices()
        assert window.combo_device.count() == 0