Index: Ringtoets/GrassCoverErosionOutwards/test/Ringtoets.GrassCoverErosionOutwards.Data.Test/GrassCoverErosionOutwardsFailureMechanismExtensionsTest.cs
===================================================================
diff -u -r1e14ee40087ad0c42f889f6ee86c13bf6d7d192b -r4c6e297466d36915591da7680c79345511dcefe0
--- Ringtoets/GrassCoverErosionOutwards/test/Ringtoets.GrassCoverErosionOutwards.Data.Test/GrassCoverErosionOutwardsFailureMechanismExtensionsTest.cs	(.../GrassCoverErosionOutwardsFailureMechanismExtensionsTest.cs)	(revision 1e14ee40087ad0c42f889f6ee86c13bf6d7d192b)
+++ Ringtoets/GrassCoverErosionOutwards/test/Ringtoets.GrassCoverErosionOutwards.Data.Test/GrassCoverErosionOutwardsFailureMechanismExtensionsTest.cs	(.../GrassCoverErosionOutwardsFailureMechanismExtensionsTest.cs)	(revision 4c6e297466d36915591da7680c79345511dcefe0)
@@ -159,5 +159,52 @@
             // Assert
             Assert.AreEqual(expectedAssessmentLevel, assessmentLevel);
         }
+
+        [Test]
+        public void GetNorm_FailureMechanismNull_ThrowsArgumentNullException()
+        {
+            // Call
+            TestDelegate test = () => GrassCoverErosionOutwardsFailureMechanismExtensions.GetNorm(null,
+                                                                                                  new AssessmentSectionStub(),
+                                                                                                  FailureMechanismCategoryType.FactorizedLowerLimitNorm);
+
+            // Assert
+            string paramName = Assert.Throws<ArgumentNullException>(test).ParamName;
+            Assert.AreEqual("failureMechanism", paramName);
+        }
+
+        [Test]
+        public void GetNorm_AssessmentSectionNull_ThrowsArgumentNullException()
+        {
+            // Setup
+            var failureMechanism = new GrassCoverErosionOutwardsFailureMechanism();
+
+            // Call
+            TestDelegate test = () => failureMechanism.GetNorm(null,
+                                                               FailureMechanismCategoryType.FactorizedLowerLimitNorm);
+
+            // Assert
+            string paramName = Assert.Throws<ArgumentNullException>(test).ParamName;
+            Assert.AreEqual("assessmentSection", paramName);
+        }
+
+        [Test]
+        public void GetNorm_InvalidAssessmentSectionCategoryType_ThrowsInvalidEnumArgumentException()
+        {
+            // Setup
+            const int invalidValue = 9999;
+
+            var assessmentSection = new AssessmentSectionStub();
+            var failureMechanism = new GrassCoverErosionOutwardsFailureMechanism();
+
+            // Call
+            TestDelegate test = () => failureMechanism.GetNorm(assessmentSection,
+                                                               (FailureMechanismCategoryType) invalidValue);
+
+            // Assert
+            string expectedMessage = $"The value of argument 'categoryType' ({invalidValue}) is invalid for Enum type '{nameof(FailureMechanismCategoryType)}'.";
+            string parameterName = TestHelper.AssertThrowsArgumentExceptionAndTestMessage<InvalidEnumArgumentException>(test, expectedMessage).ParamName;
+            Assert.AreEqual("categoryType", parameterName);
+        }
     }
 }
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