Adds tests to verify external references that are fragments aren't rewritten

Author: MaggieKimani1

test/Microsoft.OpenApi.Readers.Tests/Microsoft.OpenApi.Readers.Tests.csproj

@@ -149,6 +149,9 @@
       <EmbeddedResource Include="V3Tests\Samples\OpenApiDocument\petStoreWithTagAndSecurity.yaml">
         <CopyToOutputDirectory>Never</CopyToOutputDirectory>
       </EmbeddedResource>
+      <EmbeddedResource Include="V3Tests\Samples\OpenApiDocument\documentWithExternalRefs.yaml">
+        <CopyToOutputDirectory>Never</CopyToOutputDirectory>
+      </EmbeddedResource>
       <EmbeddedResource Include="V3Tests\Samples\OpenApiDocument\securedApi.yaml" />
       <EmbeddedResource Include="V3Tests\Samples\OpenApiEncoding\advancedEncoding.yaml">
         <CopyToOutputDirectory>Never</CopyToOutputDirectory>

test/Microsoft.OpenApi.Readers.Tests/V3Tests/OpenApiDocumentTests.cs

@@ -6,6 +6,7 @@
 using System.Globalization;
 using System.IO;
 using System.Linq;
+using System.Text;
 using System.Threading;
 using FluentAssertions;
 using Microsoft.OpenApi.Any;
@@ -1327,5 +1328,24 @@ public void HeaderParameterShouldAllowExample()
                     });
             }
         }
+
+        [Fact]
+        public void DoesNotChangeExternalReferences()
+        {
+            // Arrange
+            using var stream = Resources.GetStream(Path.Combine(SampleFolderPath, "documentWithExternalRefs.yaml"));
+            
+            // Act
+            var doc = new OpenApiStreamReader(
+                new OpenApiReaderSettings { ReferenceResolution = ReferenceResolutionSetting.DoNotResolveReferences})
+                .Read(stream, out var diagnostic);
+
+            var externalRef = doc.Components.Schemas["Nested"].Properties["AnyOf"].AnyOf.First().Reference.ReferenceV3;
+            var externalRef2 = doc.Components.Schemas["Nested"].Properties["AnyOf"].AnyOf.Last().Reference.ReferenceV3;
+
+            // Assert
+            Assert.Equal("file:///C:/MySchemas.json#/definitions/ArrayObject", externalRef);
+            Assert.Equal("../foo/schemas.yaml#/components/schemas/Number", externalRef2);
+        }
     }
 }

test/Microsoft.OpenApi.Readers.Tests/V3Tests/Samples/OpenApiDocument/documentWithExternalRefs.yaml

@@ -0,0 +1,16 @@
+    openapi: 3.0.1
+    info:
+      title: anyOf-oneOf
+      license:
+        name: MIT
+      version: 1.0.0
+    paths: { }
+    components:
+      schemas:
+        Nested:
+          type: object
+          properties:
+            AnyOf:
+              anyOf:
+                - $ref: file:///C:/MySchemas.json#/definitions/ArrayObject
+                - $ref: ../foo/schemas.yaml#/components/schemas/Number