diff --git a/tests/test_meshkernel_utils.py b/tests/test_meshkernel_utils.py
index 8dca2a35..50f23df2 100644
--- a/tests/test_meshkernel_utils.py
+++ b/tests/test_meshkernel_utils.py
@@ -1,17 +1,30 @@
+from enum import IntEnum
+from unittest.mock import MagicMock
+
 import pytest
 import shapely.geometry as sg
 
 from xugrid import meshkernel_utils as mku
+from xugrid.constants import MissingOptionalModule
 
 from . import requires_meshkernel
 
 try:
     import meshkernel as mk
+
 except ImportError:
-    pass
+    mk = MagicMock()
+    mk.RefinementType = IntEnum(
+        "RefinementType", ["WAVE_COURANT", "REFINEMENT_LEVELS", "RIDGE_DETECTION"]
+    )
+
+
+class Dummy(IntEnum):
+    A = 1
+    B = 2
+    C = 3
 
 
-@requires_meshkernel
 def test_either_string_or_enum():
     assert (
         mku.either_string_or_enum("wave_courant", mk.RefinementType)
@@ -28,7 +41,7 @@ def test_either_string_or_enum():
     with pytest.raises(ValueError, match="Invalid option"):
         mku.either_string_or_enum("none", mk.RefinementType)
     with pytest.raises(TypeError, match="Option should be one of"):
-        mku.either_string_or_enum(mk.AveragingMethod.MAX, mk.RefinementType)
+        mku.either_string_or_enum(Dummy.A, mk.RefinementType)
 
 
 @requires_meshkernel
@@ -42,3 +55,9 @@ def test_to_geometry_list():
     )
     actual = mku.to_geometry_list(polygon)
     assert isinstance(actual, mk.GeometryList)
+
+
+def test_missing_optional_module():
+    abc = MissingOptionalModule("abc")
+    with pytest.raises(ImportError, match="abc is required for this functionality"):
+        abc.attr