diff --git a/src/logic/tile/tiles/SensorLineChartTile.py b/src/logic/tile/tiles/SensorLineChartTile.py
index bc6c538bfcdde4674c3b99d0f22d81e1a08c8521..233f5bdcc09052f97d5ea636114017606addf652 100644
--- a/src/logic/tile/tiles/SensorLineChartTile.py
+++ b/src/logic/tile/tiles/SensorLineChartTile.py
@@ -183,7 +183,7 @@ class SensorLineChartTile(Tile):
             title = f'{title} - {days} days'
 
         warningSettings = self._settings['outdatedValueWarning']
-        timeSinceLastValue = self.__get_time_since_last_value(warningSettings, data)
+        timeSinceLastValue = self._get_time_since_last_value(warningSettings, data)
         if warningSettings['enableNotificationViaPushbullet']:
             self.__send_notification(warningSettings, data['sensorInfo'], data['deviceInfo'], timeSinceLastValue)
 
@@ -205,7 +205,7 @@ class SensorLineChartTile(Tile):
                                     showAxes=self._settings['showAxes'],
                                     timeSinceLastValue=timeSinceLastValue)
 
-    def __get_time_since_last_value(self, warningSettings: Dict, data):
+    def _get_time_since_last_value(self, warningSettings: Dict, data):
         timeAgo = ''
 
         if not warningSettings['enable']:
diff --git a/test/logic/tile/tiles/TestSensorLineChartTile.py b/test/logic/tile/tiles/TestSensorLineChartTile.py
index abe0cafb3b3553d20ce808628ed3500cd9956f56..9cf926989e52f105595534413b205bbd661f8dc9 100644
--- a/test/logic/tile/tiles/TestSensorLineChartTile.py
+++ b/test/logic/tile/tiles/TestSensorLineChartTile.py
@@ -1,8 +1,7 @@
 import datetime
+from unittest import mock
 from unittest.mock import MagicMock
 
-import pytest
-
 from logic.tile.tiles.SensorLineChartTile import SensorLineChartTile, SensorType
 
 
@@ -168,3 +167,40 @@ class TestPrepareGhostTrace:
         x = []
         y = []
         assert tile._prepare_ghost_trace(-10, x, y) == ([], [])
+
+
+class TestGetTimeSinceLastValue:
+    def __get_warning_settings(self, enable: bool):
+        return {
+            'enable': enable,
+            'limitInSeconds': 10,
+            'enableNotificationViaPushbullet': False,
+            'pushbulletToken': None
+        }
+
+    def test_warnings_disabled_returns_empty_string(self):
+        tile = SensorLineChartTile('mySensorTile', example_settings(False), 10)
+
+        warningSettings = self.__get_warning_settings(False)
+        data = {'latestTime': SensorLineChartTile.DATETIME_UNIX_TIMESTAMP_START}
+
+        assert tile._get_time_since_last_value(warningSettings, data) == ''
+
+    def test_warnings_enabled_no_outdated_value_returns_empty_string(self):
+        tile = SensorLineChartTile('mySensorTile', example_settings(False), 10)
+
+        warningSettings = self.__get_warning_settings(True)
+        data = {'latestTime': datetime.datetime.now()}
+
+        assert tile._get_time_since_last_value(warningSettings, data) == ''
+
+    @mock.patch('logic.tile.tiles.SensorLineChartTile.datetime')
+    def test_warnings_enabled_outdated_value_returns_human_readable_string(self, datetimeMock):
+        tile = SensorLineChartTile('mySensorTile', example_settings(False), 10)
+
+        datetimeMock.now.return_value = datetime.datetime(year=2021, month=1, day=1, hour=12, minute=00, second=00)
+
+        warningSettings = self.__get_warning_settings(True)
+        data = {'latestTime': datetime.datetime(year=2021, month=1, day=1, hour=11, minute=00, second=00)}
+
+        assert tile._get_time_since_last_value(warningSettings, data) == '1 hour ago'