diff --git a/X10D.Tests/src/Net/IPAddressTests.cs b/X10D.Tests/src/Net/IPAddressTests.cs
index ac86bf6..443d6fb 100644
--- a/X10D.Tests/src/Net/IPAddressTests.cs
+++ b/X10D.Tests/src/Net/IPAddressTests.cs
@@ -29,6 +29,13 @@ public class IPAddressTests
         Assert.IsFalse(_ipv6Address.IsIPv4());
     }
 
+    [TestMethod]
+    public void IsIPv4_ShouldThrowArgumentNullException_GivenNullAddress()
+    {
+        IPAddress address = null!;
+        Assert.ThrowsException<ArgumentNullException>(() => address.IsIPv4());
+    }
+
     [TestMethod]
     public void IsIPv6_ShouldBeFalse_GivenIPv4()
     {
@@ -40,4 +47,11 @@ public class IPAddressTests
     {
         Assert.IsTrue(_ipv6Address.IsIPv6());
     }
+
+    [TestMethod]
+    public void IsIPv6_ShouldThrowArgumentNullException_GivenNullAddress()
+    {
+        IPAddress address = null!;
+        Assert.ThrowsException<ArgumentNullException>(() => address.IsIPv6());
+    }
 }