add some comments for Operation generater and change Tags unit test name

src/Microsoft.OpenApi.OData.Reader/Generator/OpenApiOperationGenerator.cs

@@ -668,6 +668,12 @@ namespace Microsoft.OpenApi.OData.Generator
             return operation;
         }
 
+        /// <summary>
+        /// Create a <see cref="OpenApiOperation"/> for a <see cref="IEdmOperationImport"/>.
+        /// </summary>
+        /// <param name="context">The OData context.</param>
+        /// <param name="operationImport">The Edm operation import.</param>
+        /// <returns>The created <see cref="OpenApiOperation"/>.</returns>
         public static OpenApiOperation CreateOperation(this ODataContext context,
             IEdmOperationImport operationImport)
         {

src/Microsoft.OpenApi.OData.Reader/Generator/OpenApiPathItemGenerator.cs

@@ -51,6 +51,7 @@ namespace Microsoft.OpenApi.OData.Generator
                         var entityPathItem = context.CreateEntityPathItem(entitySet);
                         pathItems.Add(entityPathName, entityPathItem);
 
+                        // bound operations to entity set or entity
                         foreach (var item in context.CreateOperationPathItems(entitySet))
                         {
                             pathItems.Add(item.Key, item.Value);
@@ -63,6 +64,7 @@ namespace Microsoft.OpenApi.OData.Generator
                         var singletonPathItem = context.CreateSingletonPathItem(singleton);
                         pathItems.Add(singletonPathName, singletonPathItem);
 
+                        // bound operations to singleton
                         foreach (var item in context.CreateOperationPathItems(singleton))
                         {
                             pathItems.Add(item.Key, item.Value);

src/Microsoft.OpenApi.OData.Reader/Generator/OpenApiTagGenerator.cs

@@ -5,7 +5,6 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
-using System.Linq;
 using Microsoft.OData.Edm;
 using Microsoft.OpenApi.Models;
 

test/Microsoft.OpenAPI.OData.Reader.Tests/Generator/OpenApiTagGeneratorTests.cs

@@ -23,7 +23,7 @@ namespace Microsoft.OpenApi.OData.Generator.Tests
         }
 
         [Fact]
-        public void CreateTagsReturnsNullForEmptyModel()
+        public void CreateTagsReturnsEmptyTagsForEmptyModel()
         {
             // Arrange
             ODataContext context = new ODataContext(EdmModelHelper.EmptyModel);