add unit test for OpenApiDocumentGenerator

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

@@ -46,11 +46,17 @@ namespace Microsoft.OpenApi.OData.Generator
                 // It allows defining responses that can be reused across operations of the service.
                 Responses = context.CreateResponses(),
 
+                // Make others as null.
                 RequestBodies = null,
+
                 Examples = null,
+
                 SecuritySchemes = null,
+
                 Links = null,
+
                 Callbacks = null,
+
                 Extensions = null
             };
         }

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

@@ -46,7 +46,11 @@ namespace Microsoft.OpenApi.OData.Generator
 
                 Paths = context.CreatePaths(),
 
-                Components = context.CreateComponents()
+                Components = context.CreateComponents(),
+
+                SecurityRequirements = null,
+
+                ExternalDocs = null
             };
         }
     }

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

@@ -78,7 +78,7 @@ namespace Microsoft.OpenApi.OData.Generator
             // TODO: https://github.com/Microsoft/OpenAPI.NET.OData/issues/2
 
             //  or the entity container
-            if (context.Model.EntityContainer != null)
+            if (context.EntityContainer != null)
             {
                 string longDescription = context.Model.GetLongDescriptionAnnotation(context.Model.EntityContainer);
                 if (longDescription != null)

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

@@ -36,7 +36,7 @@ namespace Microsoft.OpenApi.OData.Generator
             // and it optionally can contain the field description, whose value is the value of the unqualified annotation
             // Core.Description of the entity set or singleton.
             IList<OpenApiTag> tags = new List<OpenApiTag>();
-            if (context.Model.EntityContainer != null)
+            if (context.EntityContainer != null)
             {
                 foreach (IEdmEntityContainerElement element in context.Model.EntityContainer.Elements)
                 {
@@ -81,8 +81,7 @@ namespace Microsoft.OpenApi.OData.Generator
                 }
             }
 
-            // Tags is optional.
-            return tags.Any() ? tags : null;
+            return tags;
         }
 
         private static OpenApiTag CreateOperationImportTag(this ODataContext context, IEdmOperationImport operationImport)

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

@@ -0,0 +1,48 @@
+// ------------------------------------------------------------
+//  Copyright (c) Microsoft Corporation.  All rights reserved.
+//  Licensed under the MIT License (MIT). See LICENSE in the repo root for license information.
+// ------------------------------------------------------------
+
+using System;
+using Microsoft.OData.Edm;
+using Microsoft.OpenApi.OData.Tests;
+using Xunit;
+
+namespace Microsoft.OpenApi.OData.Generator.Tests
+{
+    public class OpenApiDocumentGeneratorTest
+    {
+        [Fact]
+        public void CreateDocumentThrowArgumentNullContext()
+        {
+            // Arrange
+            ODataContext context = null;
+
+            // Act & Assert
+            Assert.Throws<ArgumentNullException>("context", () => context.CreateDocument());
+        }
+
+        [Fact]
+        public void CreateDocumentReturnsForEmptyModel()
+        {
+            // Arrange
+            IEdmModel model = EdmModelHelper.EmptyModel;
+            ODataContext context = new ODataContext(model);
+
+            // Act
+            var document = context.CreateDocument();
+
+            // Assert
+            Assert.NotNull(document);
+            Assert.Equal("3.0.0", document.SpecVersion.ToString());
+            Assert.NotNull(document.Info);
+            Assert.NotNull(document.Tags);
+            Assert.NotNull(document.Servers);
+            Assert.NotNull(document.Paths);
+            Assert.NotNull(document.Components);
+
+            Assert.Null(document.ExternalDocs);
+            Assert.Null(document.SecurityRequirements);
+        }
+    }
+}

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

@@ -5,7 +5,6 @@
 
 using System;
 using System.Linq;
-using Microsoft.OData.Edm;
 using Microsoft.OpenApi.OData.Tests;
 using Xunit;