diff --git a/functions/variable_wrapper.py b/functions/variable_wrapper.py
index d3f8a2d..536bd6c 100644
--- a/functions/variable_wrapper.py
+++ b/functions/variable_wrapper.py
@@ -97,6 +97,10 @@ def set_variable(key: str, value: str, scope: str = "project") -> None:
     var_name = f"sn_{key}"
 
     if scope == "project":
+        current_value = get_variable(key, scope="project")
+        if current_value == value:
+            return
+
         project = QgsProject.instance()
         QgsExpressionContextUtils.setProjectVariable(
             project,
diff --git a/tests/test_variable_wrapper.py b/tests/test_variable_wrapper.py
new file mode 100644
index 0000000..df64715
--- /dev/null
+++ b/tests/test_variable_wrapper.py
@@ -0,0 +1,56 @@
+import unittest
+from unittest.mock import patch
+
+from sn_basis.functions import variable_wrapper
+
+
+class _Scope:
+    def __init__(self, value: str):
+        self._value = value
+
+    def variable(self, _name: str) -> str:
+        return self._value
+
+
+class TestVariableWrapper(unittest.TestCase):
+
+    @patch("sn_basis.functions.variable_wrapper.QgsProject.instance")
+    @patch("sn_basis.functions.variable_wrapper.QgsExpressionContextUtils.setProjectVariable")
+    @patch("sn_basis.functions.variable_wrapper.QgsExpressionContextUtils.projectScope")
+    def test_set_variable_project_noop_write_is_skipped(
+        self,
+        mock_project_scope,
+        mock_set_project_variable,
+        mock_project_instance,
+    ):
+        mock_project_instance.return_value = object()
+        mock_project_scope.return_value = _Scope("layer_1")
+
+        variable_wrapper.set_variable("verfahrensgebiet_layer", "layer_1", scope="project")
+
+        mock_set_project_variable.assert_not_called()
+
+    @patch("sn_basis.functions.variable_wrapper.QgsProject.instance")
+    @patch("sn_basis.functions.variable_wrapper.QgsExpressionContextUtils.setProjectVariable")
+    @patch("sn_basis.functions.variable_wrapper.QgsExpressionContextUtils.projectScope")
+    def test_set_variable_project_changed_value_is_written(
+        self,
+        mock_project_scope,
+        mock_set_project_variable,
+        mock_project_instance,
+    ):
+        fake_project = object()
+        mock_project_instance.return_value = fake_project
+        mock_project_scope.return_value = _Scope("old_value")
+
+        variable_wrapper.set_variable("verfahrensgebiet_layer", "new_value", scope="project")
+
+        mock_set_project_variable.assert_called_once_with(
+            fake_project,
+            "sn_verfahrensgebiet_layer",
+            "new_value",
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tests/test_verfahrensgebiet_manager.py b/tests/test_verfahrensgebiet_manager.py
new file mode 100644
index 0000000..1ee5bc9
--- /dev/null
+++ b/tests/test_verfahrensgebiet_manager.py
@@ -0,0 +1,39 @@
+import unittest
+from unittest.mock import patch
+
+from sn_basis.functions import verfahrensgebiet_manager
+
+
+class _Scope:
+    def __init__(self, value: str):
+        self._value = value
+
+    def variable(self, _name: str) -> str:
+        return self._value
+
+
+class TestVerfahrensgebietManager(unittest.TestCase):
+
+    @patch("sn_basis.functions.verfahrensgebiet_manager._find_verfahrensgebiet_layer")
+    @patch("sn_basis.functions.variable_wrapper.QgsProject.instance")
+    @patch("sn_basis.functions.variable_wrapper.QgsExpressionContextUtils.setProjectVariable")
+    @patch("sn_basis.functions.variable_wrapper.QgsExpressionContextUtils.projectScope")
+    def test_update_without_layer_does_not_write_when_already_empty(
+        self,
+        mock_project_scope,
+        mock_set_project_variable,
+        mock_project_instance,
+        mock_find_layer,
+    ):
+        mock_find_layer.return_value = (None, None)
+        mock_project_instance.return_value = object()
+        mock_project_scope.return_value = _Scope("")
+
+        result = verfahrensgebiet_manager._update_verfahrensgebiet_from_project()
+
+        self.assertFalse(result)
+        mock_set_project_variable.assert_not_called()
+
+
+if __name__ == "__main__":
+    unittest.main()