diff --git a/X10D.Tests/src/Text/EnumerableTests.cs b/X10D.Tests/src/Text/EnumerableTests.cs
index 540a121..f498f5c 100644
--- a/X10D.Tests/src/Text/EnumerableTests.cs
+++ b/X10D.Tests/src/Text/EnumerableTests.cs
@@ -44,6 +44,20 @@ public class EnumerableTests
         Assert.AreEqual(0, actualResult.Length);
     }
 
+    [TestMethod]
+    public void Grep_ShouldThrowArgumentNullException_GivenNullPattern()
+    {
+        IEnumerable<string> source = Enumerable.Empty<string>();
+        Assert.ThrowsException<ArgumentNullException>(() => source.Grep(null!));
+    }
+
+    [TestMethod]
+    public void Grep_ShouldThrowArgumentNullException_GivenNullSource()
+    {
+        IEnumerable<string> source = null!;
+        Assert.ThrowsException<ArgumentNullException>(() => source.Grep("foo"));
+    }
+
     [TestMethod]
     public void Grep_ShouldYieldNoElements_GivenNoMatchingStrings()
     {