[Sub] Write Entity Platform Tests

[switch180]

Parent Issue: #4 Zero Test Coverage

Objective

Create unit tests for all entity platforms (sensors, binary sensors, selects) covering state derivation and user actions.

Test Coverage Areas

Sensor Platform Tests

• test_receiver_temperature_sensor - Temperature state
• test_video_source_sensor - Source name and attributes
• test_audio_source_sensor - Audio source info
• test_video_signal_sensor - Signal formatting
• test_transmitter_stream_sensors - Stream state
• test_ip_address_sensor - Network info
• test_firmware_sensor - Version display

Binary Sensor Platform Tests

• test_online_sensor - Connectivity state
• test_video_streaming_sensor - Stream state detection
• test_audio_streaming_sensor - Audio state

Select Platform Tests

• test_video_source_select_options - Source list generation
• test_video_source_select_current - Current value
• test_video_source_select_action - Join/leave calls
• test_display_mode_select - Mode changes
• test_resolution_preset_select - Resolution selection
• test_pending_resolution_handling - Genlock mode behavior

Entity Base Tests

• test_device_info_generation - Device info structure
• test_entity_availability - Availability logic
• test_entity_attributes - Extra state attributes

Mock Strategy

# Mock coordinator with fixture data
@pytest.fixture
def mock_coordinator():
    coordinator = Mock(spec=RiverLinkDataUpdateCoordinator)
    coordinator.data = {
        "receivers": {...},
        "transmitters": {...}
    }
    return coordinator

Target Coverage

• Goal: 80%+ line coverage per platform file
• Focus: State derivation and user actions

References

• Files: sensor.py, binary_sensor.py, select.py
• Parent Issue: Zero Test Coverage - Critical Testing Infrastructure Gap #4

Priority

🟡 Medium - User-facing components