diff --git a/tests/test_gui.py b/tests/test_gui.py
index 309133f..431445a 100644
--- a/tests/test_gui.py
+++ b/tests/test_gui.py
@@ -1,19 +1,38 @@
 import unittest
+from unittest.mock import patch
 
-from pydiode.gui.common import stuck_running
+from pydiode.gui.common import ProcessPipeline
 
 
 class TestGUI(unittest.TestCase):
-    def test_stuck_running(self):
-        self.assertTrue(stuck_running([None, 0]))
-        self.assertTrue(stuck_running([None, None, 0]))
-        self.assertTrue(stuck_running([None, 0, None]))
 
-        self.assertFalse(stuck_running([0]))
-        self.assertFalse(stuck_running([None]))
+    def setUp(self):
+        self.pipeline = ProcessPipeline()
 
-        self.assertFalse(stuck_running([0, 0]))
-        self.assertFalse(stuck_running([0, None]))
-        self.assertFalse(stuck_running([0, None, None]))
-        self.assertFalse(stuck_running([0, 0, None]))
-        self.assertFalse(stuck_running([None, None]))
+    @patch.object(ProcessPipeline, "_returncodes")
+    def test_stuck_running(self, mock_returncodes):
+        # Stuck pipelines
+        mock_returncodes.return_value = [None, 0]
+        self.assertTrue(self.pipeline.stuck_running())
+        mock_returncodes.return_value = [None, None, 0]
+        self.assertTrue(self.pipeline.stuck_running())
+        mock_returncodes.return_value = [None, 0, None]
+        self.assertTrue(self.pipeline.stuck_running())
+
+        # Simple non-stuck pipelines
+        mock_returncodes.return_value = [0]
+        self.assertFalse(self.pipeline.stuck_running())
+        mock_returncodes.return_value = [None]
+        self.assertFalse(self.pipeline.stuck_running())
+
+        # Complex non-stuck pipelines
+        mock_returncodes.return_value = [0, 0]
+        self.assertFalse(self.pipeline.stuck_running())
+        mock_returncodes.return_value = [0, None]
+        self.assertFalse(self.pipeline.stuck_running())
+        mock_returncodes.return_value = [0, None, None]
+        self.assertFalse(self.pipeline.stuck_running())
+        mock_returncodes.return_value = [0, 0, None]
+        self.assertFalse(self.pipeline.stuck_running())
+        mock_returncodes.return_value = [None, None]
+        self.assertFalse(self.pipeline.stuck_running())