diff --git a/src/Microsoft.OpenApi/Services/OpenApiUrlTreeNode.cs b/src/Microsoft.OpenApi/Services/OpenApiUrlTreeNode.cs
index 296068914..30a47bdd7 100644
--- a/src/Microsoft.OpenApi/Services/OpenApiUrlTreeNode.cs
+++ b/src/Microsoft.OpenApi/Services/OpenApiUrlTreeNode.cs
@@ -47,11 +47,16 @@ public class OpenApiUrlTreeNode
         public string Segment { get; private set; }
 
         /// <summary>
-        /// Flag indicating whether the node's PathItems has operations.
+        /// Flag indicating whether the node's PathItems dictionary has operations
+        /// under a given label.
         /// </summary>
+        /// <param name="label">The name of the key for the target operations
+        /// in the node's PathItems dictionary.</param>
         /// <returns>true or false.</returns>
         public bool HasOperations(string label)
         {
+            Utils.CheckArgumentNullOrEmpty(label, nameof(label));
+
             if (!(PathItems?.ContainsKey(label) ?? false))
             {
                 return false;
@@ -139,6 +144,8 @@ public OpenApiUrlTreeNode Attach(string path,
                                          string label)
         {
             Utils.CheckArgumentNullOrEmpty(label, nameof(label));
+            Utils.CheckArgumentNullOrEmpty(path, nameof(path));
+            Utils.CheckArgumentNull(pathItem, nameof(pathItem));
 
             if (path.StartsWith(RootPathSegment))
             {
diff --git a/test/Microsoft.OpenApi.Tests/Services/OpenApiUrlTreeNodeTests.cs b/test/Microsoft.OpenApi.Tests/Services/OpenApiUrlTreeNodeTests.cs
index a246c66ff..944e6c830 100644
--- a/test/Microsoft.OpenApi.Tests/Services/OpenApiUrlTreeNodeTests.cs
+++ b/test/Microsoft.OpenApi.Tests/Services/OpenApiUrlTreeNodeTests.cs
@@ -11,6 +11,26 @@ namespace Microsoft.OpenApi.Tests.Services
 {
     public class OpenApiUrlTreeNodeTests
     {
+        private OpenApiDocument OpenApiDocumentSample_1 => new OpenApiDocument()
+        {
+            Paths = new OpenApiPaths()
+            {
+                ["/"] = new OpenApiPathItem(),
+                ["/houses"] = new OpenApiPathItem(),
+                ["/cars"] = new OpenApiPathItem()
+            }
+        };
+
+        private OpenApiDocument OpenApiDocumentSample_2 => new OpenApiDocument()
+        {
+            Paths = new OpenApiPaths()
+            {
+                ["/"] = new OpenApiPathItem(),
+                ["/hotels"] = new OpenApiPathItem(),
+                ["/offices"] = new OpenApiPathItem()
+            }
+        };
+
         [Fact]
         public void CreateUrlSpaceWithoutOpenApiDocument()
         {
@@ -64,15 +84,7 @@ public void CreatePathWithoutRootWorks()
         [Fact]
         public void CreateMultiplePathsWorks()
         {
-            var doc = new OpenApiDocument()
-            {
-                Paths = new OpenApiPaths()
-                {
-                    ["/"] = new OpenApiPathItem(),
-                    ["/houses"] = new OpenApiPathItem(),
-                    ["/cars"] = new OpenApiPathItem()
-                }
-            };
+            var doc = OpenApiDocumentSample_1;
 
             string label = "assets";
             var rootNode = OpenApiUrlTreeNode.Create(doc, label);
@@ -89,25 +101,9 @@ public void CreateMultiplePathsWorks()
         [Fact]
         public void AttachDocumentWorks()
         {
-            var doc1 = new OpenApiDocument()
-            {
-                Paths = new OpenApiPaths()
-                {
-                    ["/"] = new OpenApiPathItem(),
-                    ["/houses"] = new OpenApiPathItem(),
-                    ["/cars"] = new OpenApiPathItem()
-                }
-            };
+            var doc1 = OpenApiDocumentSample_1;
 
-            var doc2 = new OpenApiDocument()
-            {
-                Paths = new OpenApiPaths()
-                {
-                    ["/"] = new OpenApiPathItem(),
-                    ["/hotels"] = new OpenApiPathItem(),
-                    ["/offices"] = new OpenApiPathItem()
-                }
-            };
+            var doc2 = OpenApiDocumentSample_2;
 
             var label1 = "personal";
             var label2 = "business";
@@ -123,15 +119,7 @@ public void AttachDocumentWorks()
         [Fact]
         public void AttachPathWorks()
         {
-            var doc = new OpenApiDocument()
-            {
-                Paths = new OpenApiPaths()
-                {
-                    ["/"] = new OpenApiPathItem(),
-                    ["/houses"] = new OpenApiPathItem(),
-                    ["/cars"] = new OpenApiPathItem()
-                }
-            };
+            var doc = OpenApiDocumentSample_1;
 
             var label1 = "personal";
             var rootNode = OpenApiUrlTreeNode.Create(doc, label1);
@@ -335,96 +323,10 @@ public void SegmentIsParameterWorks()
             Assert.Equal("{apartment-id}", rootNode.Children["houses"].Children["apartments"].Children["{apartment-id}"].Segment);
         }
 
-        [Fact]
-        public void ThrowsArgumentExceptionForDuplicateLabels()
-        {
-            var doc1 = new OpenApiDocument()
-            {
-                Paths = new OpenApiPaths()
-                {
-                    ["/"] = new OpenApiPathItem(),
-                    ["/houses"] = new OpenApiPathItem(),
-                    ["/cars"] = new OpenApiPathItem()
-                }
-            };
-
-            var doc2 = new OpenApiDocument()
-            {
-                Paths = new OpenApiPaths()
-                {
-                    ["/"] = new OpenApiPathItem(),
-                    ["/hotels"] = new OpenApiPathItem(),
-                    ["/offices"] = new OpenApiPathItem()
-                }
-            };
-
-            var label1 = "personal";
-            var rootNode = OpenApiUrlTreeNode.Create(doc1, label1);
-
-            Assert.Throws<ArgumentException>(() => rootNode.Attach(doc2, label1));
-        }
-
-        [Fact]
-        public void ThrowsArgumentNullExceptionForNullArgumentsInCreateMethod()
-        {
-            var doc = new OpenApiDocument()
-            {
-                Paths = new OpenApiPaths()
-                {
-                    ["/"] = new OpenApiPathItem(),
-                    ["/houses"] = new OpenApiPathItem(),
-                    ["/cars"] = new OpenApiPathItem()
-                }
-            };
-
-            Assert.Throws<ArgumentNullException>(() => OpenApiUrlTreeNode.Create(doc, ""));
-            Assert.Throws<ArgumentNullException>(() => OpenApiUrlTreeNode.Create(doc, null));
-            Assert.Throws<ArgumentNullException>(() => OpenApiUrlTreeNode.Create(null, "beta"));
-        }
-
-        [Fact]
-        public void ThrowsArgumentNullExceptionForNullArgumentsInAttachMethod()
-        {
-            var doc1 = new OpenApiDocument()
-            {
-                Paths = new OpenApiPaths()
-                {
-                    ["/"] = new OpenApiPathItem(),
-                    ["/houses"] = new OpenApiPathItem(),
-                    ["/cars"] = new OpenApiPathItem()
-                }
-            };
-
-            var doc2 = new OpenApiDocument()
-            {
-                Paths = new OpenApiPaths()
-                {
-                    ["/"] = new OpenApiPathItem(),
-                    ["/hotels"] = new OpenApiPathItem(),
-                    ["/offices"] = new OpenApiPathItem()
-                }
-            };
-
-            var label1 = "personal";
-            var rootNode = OpenApiUrlTreeNode.Create(doc1, label1);
-
-            Assert.Throws<ArgumentNullException>(() => rootNode.Attach(doc2, ""));
-            Assert.Throws<ArgumentNullException>(() => rootNode.Attach(doc2, null));
-            Assert.Throws<ArgumentNullException>(() => rootNode.Attach(null, "beta"));
-        }
-
         [Fact]
         public void AdditionalDataWorks()
         {
-            var doc = new OpenApiDocument()
-            {
-                Paths = new OpenApiPaths()
-                {
-                    ["/"] = new OpenApiPathItem(),
-                    ["/houses"] = new OpenApiPathItem(),
-                    ["/cars"] = new OpenApiPathItem()
-                }
-            };
+            var doc = OpenApiDocumentSample_1;
 
             var label = "personal";
             var rootNode = OpenApiUrlTreeNode.Create(doc, label);
@@ -476,5 +378,70 @@ public void AdditionalDataWorks()
                     Assert.Equal("Convertible", item);
                 });
         }
+
+        [Fact]
+        public void ThrowsArgumentExceptionForDuplicateLabels()
+        {
+            var doc1 = OpenApiDocumentSample_1;
+
+            var doc2 = OpenApiDocumentSample_2;
+
+            var label1 = "personal";
+            var rootNode = OpenApiUrlTreeNode.Create(doc1, label1);
+
+            Assert.Throws<ArgumentException>(() => rootNode.Attach(doc2, label1));
+        }
+
+        [Fact]
+        public void ThrowsArgumentNullExceptionForNullOrEmptyArgumentsInCreateMethod()
+        {
+            var doc = OpenApiDocumentSample_1;
+
+            Assert.Throws<ArgumentNullException>(() => OpenApiUrlTreeNode.Create(doc, ""));
+            Assert.Throws<ArgumentNullException>(() => OpenApiUrlTreeNode.Create(doc, null));
+            Assert.Throws<ArgumentNullException>(() => OpenApiUrlTreeNode.Create(null, "beta"));
+            Assert.Throws<ArgumentNullException>(() => OpenApiUrlTreeNode.Create(null, null));
+            Assert.Throws<ArgumentNullException>(() => OpenApiUrlTreeNode.Create(null, ""));
+        }
+
+        [Fact]
+        public void ThrowsArgumentNullExceptionForNullOrEmptyArgumentsInAttachMethod()
+        {
+            var doc1 = OpenApiDocumentSample_1;
+
+            var doc2 = OpenApiDocumentSample_2;
+
+            var label1 = "personal";
+            var rootNode = OpenApiUrlTreeNode.Create(doc1, label1);
+
+            Assert.Throws<ArgumentNullException>(() => rootNode.Attach(doc2, ""));
+            Assert.Throws<ArgumentNullException>(() => rootNode.Attach(doc2, null));
+            Assert.Throws<ArgumentNullException>(() => rootNode.Attach(null, "beta"));
+            Assert.Throws<ArgumentNullException>(() => rootNode.Attach(null, null));
+            Assert.Throws<ArgumentNullException>(() => rootNode.Attach(null, ""));
+        }
+
+        [Fact]
+        public void ThrowsArgumentNullExceptionForNullOrEmptyArgumentInHasOperationsMethod()
+        {
+            var doc = OpenApiDocumentSample_1;
+
+            var label = "personal";
+            var rootNode = OpenApiUrlTreeNode.Create(doc, label);
+
+            Assert.Throws<ArgumentNullException>(() => rootNode.HasOperations(null));
+            Assert.Throws<ArgumentNullException>(() => rootNode.HasOperations(""));
+        }
+
+        [Fact]
+        public void ThrowsArgumentNullExceptionForNullArgumentInAddAdditionalDataMethod()
+        {
+            var doc = OpenApiDocumentSample_1;
+
+            var label = "personal";
+            var rootNode = OpenApiUrlTreeNode.Create(doc, label);
+
+            Assert.Throws<ArgumentNullException>(() => rootNode.AddAdditionalData(null));
+        }
     }
 }