diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..6eb3df5
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,2 @@
+[tool.pytest.ini_options]
+asyncio_mode = "auto"
diff --git a/tests/localthings/__init__.py b/tests/localthings/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/localthings/conftest.py b/tests/localthings/conftest.py
new file mode 100644
index 0000000..d98a3e6
--- /dev/null
+++ b/tests/localthings/conftest.py
@@ -0,0 +1,98 @@
+"""Shared fixtures for localthings component tests."""
+from __future__ import annotations
+
+import json
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+from pytest_homeassistant_custom_component.common import MockConfigEntry
+
+# Point HA's config dir at the repo root so the loader mounts custom_components/
+# from the project into sys.path — otherwise IntegrationNotFound is raised.
+PROJECT_ROOT = str(Path(__file__).resolve().parents[2])
+
+
+@pytest.fixture
+def hass_config_dir() -> str:
+    """Override to let HA's loader find custom_components/localthings."""
+    return PROJECT_ROOT
+
+
+@pytest.fixture(autouse=True)
+def auto_enable_custom_integrations(enable_custom_integrations):
+    """Automatically enable custom integrations for all localthings tests.
+
+    pytest-homeassistant-custom-component caches an empty custom-component
+    dict during HA startup. This autouse fixture calls the upstream
+    enable_custom_integrations fixture which pops that cache entry, forcing
+    a re-discovery that finds custom_components/localthings.
+    """
+    return enable_custom_integrations
+
+
+from custom_components.localthings.const import (
+    CONF_CERT_PEM, CONF_HOST, CONF_KEY_PEM, CONF_PORT, DOMAIN,
+)
+
+FIXTURES = Path(__file__).resolve().parent.parent / 'fixtures'
+
+MOCK_HOST = '10.0.0.254'
+MOCK_PORT = 49154
+MOCK_SERIAL = 'TEST-SERIAL-001'
+MOCK_CERT_PEM = '-----BEGIN CERTIFICATE-----\nTEST\n-----END CERTIFICATE-----'
+MOCK_KEY_PEM = '-----BEGIN PRIVATE KEY-----\nTEST\n-----END PRIVATE KEY-----'
+
+ENTRY_DATA = {
+    CONF_HOST: MOCK_HOST,
+    CONF_PORT: MOCK_PORT,
+    CONF_CERT_PEM: MOCK_CERT_PEM,
+    CONF_KEY_PEM: MOCK_KEY_PEM,
+}
+
+
+def _load_fridge_resources() -> dict:
+    from samsung_appliance.batch import parse_device0_batch
+    data = json.loads((FIXTURES / 'refrigerator_device.json').read_text())
+    return parse_device0_batch(data['device0'])
+
+
+@pytest.fixture
+def fridge_resources():
+    return _load_fridge_resources()
+
+
+@pytest.fixture
+def mock_probe():
+    """Patch _probe_and_validate to succeed without a real DTLS connection."""
+    with patch(
+        'custom_components.localthings.config_flow._probe_and_validate',
+        return_value={'port': MOCK_PORT, 'serial': MOCK_SERIAL},
+    ) as m:
+        yield m
+
+
+@pytest.fixture
+def mock_coordinator_session(fridge_resources):
+    """Patch coordinator's blocking session methods so no real DTLS is needed."""
+    with (
+        patch('custom_components.localthings.coordinator.LocalThingsCoordinator._connect_session'),
+        patch(
+            'custom_components.localthings.coordinator.LocalThingsCoordinator._poll_once',
+            return_value=fridge_resources,
+        ),
+        patch('custom_components.localthings.coordinator.LocalThingsCoordinator._close_session'),
+    ):
+        yield
+
+
+@pytest.fixture
+def mock_entry(hass):
+    """A MockConfigEntry added to hass, ready for async_setup."""
+    entry = MockConfigEntry(
+        domain=DOMAIN,
+        data=ENTRY_DATA,
+        unique_id=f'localthings_{MOCK_SERIAL}',
+    )
+    entry.add_to_hass(hass)
+    return entry
diff --git a/tests/localthings/test_config_flow.py b/tests/localthings/test_config_flow.py
new file mode 100644
index 0000000..baee55c
--- /dev/null
+++ b/tests/localthings/test_config_flow.py
@@ -0,0 +1,100 @@
+"""Tests for the localthings config flow."""
+from __future__ import annotations
+
+from unittest.mock import patch
+
+import pytest
+from homeassistant.core import HomeAssistant
+from homeassistant.data_entry_flow import FlowResultType
+from pytest_homeassistant_custom_component.common import MockConfigEntry
+
+from custom_components.localthings.const import (
+    CONF_CERT_PEM, CONF_HOST, CONF_KEY_PEM, CONF_PORT, DOMAIN,
+)
+
+from .conftest import (
+    ENTRY_DATA, MOCK_CERT_PEM, MOCK_HOST, MOCK_KEY_PEM, MOCK_PORT, MOCK_SERIAL,
+)
+
+
+async def test_form_first_device(hass: HomeAssistant) -> None:
+    """First device: form asks for host, cert, and key."""
+    result = await hass.config_entries.flow.async_init(
+        DOMAIN, context={'source': 'user'}
+    )
+    assert result['type'] == FlowResultType.FORM
+    assert result['step_id'] == 'user'
+    assert CONF_CERT_PEM in result['data_schema'].schema
+    assert CONF_KEY_PEM in result['data_schema'].schema
+
+
+async def test_form_second_device_reuses_creds(hass: HomeAssistant) -> None:
+    """Second device: form only asks for host; cert/key schema fields absent."""
+    existing = MockConfigEntry(domain=DOMAIN, data=ENTRY_DATA)
+    existing.add_to_hass(hass)
+
+    result = await hass.config_entries.flow.async_init(
+        DOMAIN, context={'source': 'user'}
+    )
+    assert result['type'] == FlowResultType.FORM
+    assert CONF_CERT_PEM not in result['data_schema'].schema
+    assert CONF_KEY_PEM not in result['data_schema'].schema
+
+
+async def test_successful_setup(hass: HomeAssistant, mock_probe) -> None:
+    """Happy path: valid IP connects, entry created with discovered port."""
+    result = await hass.config_entries.flow.async_init(
+        DOMAIN, context={'source': 'user'}
+    )
+    result = await hass.config_entries.flow.async_configure(
+        result['flow_id'],
+        {CONF_HOST: MOCK_HOST, CONF_CERT_PEM: MOCK_CERT_PEM, CONF_KEY_PEM: MOCK_KEY_PEM},
+    )
+    assert result['type'] == FlowResultType.CREATE_ENTRY
+    assert result['data'][CONF_HOST] == MOCK_HOST
+    assert result['data'][CONF_PORT] == MOCK_PORT
+    assert result['data'][CONF_CERT_PEM] == MOCK_CERT_PEM
+
+
+async def test_cannot_connect(hass: HomeAssistant) -> None:
+    """Failed probe: form re-shown with cannot_connect error."""
+    from custom_components.localthings.config_flow import CannotConnect
+
+    with patch(
+        'custom_components.localthings.config_flow._probe_and_validate',
+        side_effect=CannotConnect('no port'),
+    ):
+        result = await hass.config_entries.flow.async_init(
+            DOMAIN, context={'source': 'user'}
+        )
+        result = await hass.config_entries.flow.async_configure(
+            result['flow_id'],
+            {CONF_HOST: MOCK_HOST, CONF_CERT_PEM: MOCK_CERT_PEM, CONF_KEY_PEM: MOCK_KEY_PEM},
+        )
+    assert result['type'] == FlowResultType.FORM
+    assert result['errors']['base'] == 'cannot_connect'
+
+
+async def test_duplicate_device_aborted(hass: HomeAssistant, mock_probe) -> None:
+    """Second add of same serial: flow aborts.
+
+    When a device already exists the form only asks for host (cert/key are
+    reused), so we only submit CONF_HOST in the second configure call.
+    """
+    existing = MockConfigEntry(
+        domain=DOMAIN,
+        data=ENTRY_DATA,
+        unique_id=f'localthings_{MOCK_SERIAL}',
+    )
+    existing.add_to_hass(hass)
+
+    result = await hass.config_entries.flow.async_init(
+        DOMAIN, context={'source': 'user'}
+    )
+    # Second-device form only has CONF_HOST; cert/key are reused from existing.
+    result = await hass.config_entries.flow.async_configure(
+        result['flow_id'],
+        {CONF_HOST: MOCK_HOST},
+    )
+    assert result['type'] == FlowResultType.ABORT
+    assert result['reason'] == 'already_configured'
diff --git a/tests/localthings/test_coordinator.py b/tests/localthings/test_coordinator.py
new file mode 100644
index 0000000..0ae6d21
--- /dev/null
+++ b/tests/localthings/test_coordinator.py
@@ -0,0 +1,74 @@
+"""Tests for the LocalThingsCoordinator."""
+from __future__ import annotations
+
+from datetime import timedelta
+from unittest.mock import patch
+
+import pytest
+from homeassistant.core import HomeAssistant
+
+from custom_components.localthings.const import (
+    ACTIVE_INTERVAL_S, DOMAIN, IDLE_INTERVAL_S,
+)
+from custom_components.localthings.coordinator import LocalThingsCoordinator
+
+from .conftest import ENTRY_DATA, MOCK_SERIAL
+
+
+async def test_first_refresh_runs_discovery(
+    hass: HomeAssistant, mock_entry, mock_coordinator_session
+) -> None:
+    """After first refresh, coordinator.bound is populated."""
+    await hass.config_entries.async_setup(mock_entry.entry_id)
+    await hass.async_block_till_done()
+
+    coordinator: LocalThingsCoordinator = hass.data[DOMAIN][mock_entry.entry_id]
+    assert coordinator.bound
+    assert coordinator.data
+
+
+async def test_device_info_populated(
+    hass: HomeAssistant, mock_entry, mock_coordinator_session
+) -> None:
+    """device_info is set from discovered resources after first refresh."""
+    await hass.config_entries.async_setup(mock_entry.entry_id)
+    await hass.async_block_till_done()
+
+    coordinator: LocalThingsCoordinator = hass.data[DOMAIN][mock_entry.entry_id]
+    assert coordinator.device_info is not None
+    assert any(
+        DOMAIN in str(i)
+        for i in coordinator.device_info.get('identifiers', set())
+    )
+
+
+async def test_idle_interval_by_default(
+    hass: HomeAssistant, mock_entry, mock_coordinator_session
+) -> None:
+    """Interval defaults to idle when no active_when fires."""
+    await hass.config_entries.async_setup(mock_entry.entry_id)
+    await hass.async_block_till_done()
+
+    coordinator: LocalThingsCoordinator = hass.data[DOMAIN][mock_entry.entry_id]
+    assert coordinator.update_interval == timedelta(seconds=IDLE_INTERVAL_S)
+
+
+async def test_update_failed_on_persistent_poll_error(
+    hass: HomeAssistant, mock_entry
+) -> None:
+    """ConfigEntryNotReady raised when poll fails even after reconnect."""
+    from homeassistant.exceptions import ConfigEntryNotReady
+
+    with (
+        patch('custom_components.localthings.coordinator.LocalThingsCoordinator._connect_session'),
+        patch(
+            'custom_components.localthings.coordinator.LocalThingsCoordinator._poll_once',
+            side_effect=RuntimeError('connection lost'),
+        ),
+        patch('custom_components.localthings.coordinator.LocalThingsCoordinator._close_session'),
+    ):
+        result = await hass.config_entries.async_setup(mock_entry.entry_id)
+        await hass.async_block_till_done()
+
+    # Setup fails — entry should not be in hass.data
+    assert not result or mock_entry.entry_id not in hass.data.get(DOMAIN, {})
diff --git a/tests/localthings/test_sensor.py b/tests/localthings/test_sensor.py
new file mode 100644
index 0000000..dc8cb39
--- /dev/null
+++ b/tests/localthings/test_sensor.py
@@ -0,0 +1,47 @@
+"""Tests for the sensor platform."""
+from __future__ import annotations
+
+import pytest
+from homeassistant.core import HomeAssistant
+from homeassistant.helpers import entity_registry as er
+
+from custom_components.localthings.const import DOMAIN
+
+
+async def test_sensors_registered(
+    hass: HomeAssistant, mock_entry, mock_coordinator_session
+) -> None:
+    """Sensors are registered for all SensorDesc entities in the fridge fixture."""
+    await hass.config_entries.async_setup(mock_entry.entry_id)
+    await hass.async_block_till_done()
+
+    ent_reg = er.async_get(hass)
+    entries = er.async_entries_for_config_entry(ent_reg, mock_entry.entry_id)
+    sensor_entries = [e for e in entries if e.domain == 'sensor']
+    assert sensor_entries, "Expected at least one sensor entity"
+
+
+async def test_sensor_state_from_coordinator(
+    hass: HomeAssistant, mock_entry, mock_coordinator_session
+) -> None:
+    """A temperature sensor reads its value from coordinator.data.
+
+    Entity IDs are auto-generated by HA and don't embed capability path
+    segments, so we filter by the mdi:thermometer icon that the fridge
+    capability assigns to current-temperature sensors.
+    """
+    await hass.config_entries.async_setup(mock_entry.entry_id)
+    await hass.async_block_till_done()
+
+    states = hass.states.async_all('sensor')
+    temp_states = [
+        s for s in states
+        if s.attributes.get('icon') == 'mdi:thermometer'
+    ]
+    assert temp_states, (
+        f"No thermometer sensor found. Sensors: {[s.entity_id for s in states]}"
+    )
+    state = temp_states[0]
+    assert state.state not in ('unknown', 'unavailable'), (
+        f"Sensor state is {state.state}"
+    )