diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4f378e9..db1778e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -33,10 +33,16 @@ jobs:
         run: mypy src/behavior_generation_lecture_python/mdp
 
       - name: test
-        run: pytest
-
-      - name: check coverage # (less coverage required here since vizard is not tested)
-        run: pytest --cov=src --cov-fail-under=70
+        run: |
+          export DISPLAY=:99
+          Xvfb :99 &
+          pytest
+
+      - name: check coverage
+        run: |
+          export DISPLAY=:99
+          Xvfb :99 &
+          pytest --cov=src --cov-fail-under=85
 
       - name: copy notebooks to docs folder
         run: cp -r notebooks/* docs/notebooks
diff --git a/src/behavior_generation_lecture_python/finite_state_machine/traffic_light_state_machine_with_visu.py b/src/behavior_generation_lecture_python/finite_state_machine/traffic_light_state_machine_with_visu.py
index 1c5c618..d035a7a 100644
--- a/src/behavior_generation_lecture_python/finite_state_machine/traffic_light_state_machine_with_visu.py
+++ b/src/behavior_generation_lecture_python/finite_state_machine/traffic_light_state_machine_with_visu.py
@@ -26,8 +26,8 @@ class TrafficLightStateMachine(StateMachine):
     veh_go = veh_red_yellow.to(veh_green)
 
     def __init__(self, start_mainloop=True):
-        StateMachine.__init__(self)
         self.visu = VisualizeTrafficLights()
+        super().__init__(self)
         self.visu.register_button_event(self.button_press)
         self.visu.vehicle_go()
         if start_mainloop:
@@ -38,34 +38,34 @@ def on_enter_veh_yellow(self):
         time.sleep(3)
         self.visu.vehicle_prepare_to_stop()
         time.sleep(3)
-        self.run("veh_stop")
+        self.send("veh_stop")
 
     def on_enter_veh_red_ped_red_1(self):
         self.visu.vehicle_stop()
         time.sleep(2)
-        self.run("ped_go")
+        self.send("ped_go")
 
     def on_enter_veh_red_ped_green(self):
         self.visu.pedestrian_go()
         time.sleep(5)
-        self.run("ped_stop")
+        self.send("ped_stop")
 
     def on_enter_veh_red_ped_red_2(self):
         self.visu.pedestrian_stop()
         time.sleep(5)
-        self.run("veh_prepare_to_go")
+        self.send("veh_prepare_to_go")
 
     def on_enter_veh_red_yellow(self):
         self.visu.vehicle_prepare_to_go()
         time.sleep(2)
-        self.run("veh_go")
+        self.send("veh_go")
 
     def on_enter_veh_green(self):
         self.visu.vehicle_go()
 
     def button_press(self, event):
-        if self.is_veh_green:
-            self.run("veh_prepare_to_stop")
+        if self.state == "veh_green":
+            self.send("veh_prepare_to_stop")
         else:
             warnings.warn(
                 "The button only has effect if currently vehicles have green."
diff --git a/tests/finite_state_machine/test_traffic_light_state_machine_visu.py b/tests/finite_state_machine/test_traffic_light_state_machine_visu.py
index 1e427ea..97aee85 100644
--- a/tests/finite_state_machine/test_traffic_light_state_machine_visu.py
+++ b/tests/finite_state_machine/test_traffic_light_state_machine_visu.py
@@ -7,7 +7,6 @@
 )
 
 
-@pytest.mark.skipif(not os.environ.get("DISPLAY"), reason="Display required")
 def test_traffic_light_state_machine_with_visu():
     tl = traffic_light_state_machine_with_visu.TrafficLightStateMachine(
         start_mainloop=False