Index: Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Service.Test/MacroStabilityInwardsInputValidatorTest.cs
===================================================================
diff -u -r9368b3ac19481ec8b10dcea903ecdf0fab3048cf -re4e0e6f48ce1decab5f8a3831d8663abc1799fbb
--- Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Service.Test/MacroStabilityInwardsInputValidatorTest.cs	(.../MacroStabilityInwardsInputValidatorTest.cs)	(revision 9368b3ac19481ec8b10dcea903ecdf0fab3048cf)
+++ Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Service.Test/MacroStabilityInwardsInputValidatorTest.cs	(.../MacroStabilityInwardsInputValidatorTest.cs)	(revision e4e0e6f48ce1decab5f8a3831d8663abc1799fbb)
@@ -303,6 +303,56 @@
             CollectionAssert.IsEmpty(messages);
         }
 
+        [Test]
+        public void Validate_MultipleTangentLinesWithTangentLineTopAndBottomSame_ReturnsError()
+        {
+            // Setup
+            var random = new Random(21);
+            input.TangentLineNumber = random.Next(2, 50);
+            input.TangentLineZTop = (RoundedDouble) 1.5;
+            input.TangentLineZBottom = (RoundedDouble) 1.5;
+
+            // Call
+            IEnumerable<string> messages = MacroStabilityInwardsInputValidator.Validate(input).ToArray();
+
+            // Assert
+            CollectionAssert.AreEqual(new[]
+            {
+                "Het aantal tangentlijnen moet 1 zijn wanneer tangentlijn Z-boven gelijk is aan tangentlijn Z-onder."
+            }, messages);
+        }
+
+        [Test]
+        public void Validate_MultipleTangentLinesWithTangentLineTopAndBottomNotSame_ReturnsEmpty()
+        {
+            // Setup
+            var random = new Random(21);
+            input.TangentLineNumber = random.Next(2, 50);
+            input.TangentLineZTop = (RoundedDouble) 1.5;
+            input.TangentLineZBottom = (RoundedDouble) 0.2;
+
+            // Call
+            IEnumerable<string> messages = MacroStabilityInwardsInputValidator.Validate(input).ToArray();
+
+            // Assert
+            CollectionAssert.IsEmpty(messages);
+        }
+
+        [Test]
+        public void Validate_SingleTangentLineWithTangentLineTopAndBottomSame_ReturnsEmpty()
+        {
+            // Setup
+            input.TangentLineNumber = 1;
+            input.TangentLineZTop = (RoundedDouble) 1.59;
+            input.TangentLineZBottom = (RoundedDouble) 1.59;
+
+            // Call
+            IEnumerable<string> messages = MacroStabilityInwardsInputValidator.Validate(input).ToArray();
+
+            // Assert
+            CollectionAssert.IsEmpty(messages);
+        }
+
         private static IEnumerable<TestCaseData> SurfacelineNotOnMacroStabilityInwardsSoilProfile2D()
         {
             yield return new TestCaseData(