Add test to validate

Author: MaggieKimani1

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

@@ -42,14 +42,14 @@
       <DependentUpon>OpenApiCallbackReferenceTests.cs</DependentUpon>
     </None>
 
+    <None Update="Models\Samples\docWithDollarId.yaml">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+      
     <None Update="Models\Samples\docWithReusableWebhooks.yaml">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </None>
 
     <None Update="PublicApi\PublicApi.approved.txt" CopyToOutputDirectory="Always" />
   </ItemGroup>
-
-  <ItemGroup>
-    <Folder Include="Models\Samples\" />
-  </ItemGroup>
 </Project>

test/Microsoft.OpenApi.Tests/Models/OpenApiDocumentTests.cs

@@ -1642,5 +1642,54 @@ public void SerializeV31DocumentWithRefsInWebhooksWorks()
             var actual = stringWriter.ToString();
             actual.MakeLineBreaksEnvironmentNeutral().Should().BeEquivalentTo(expected.MakeLineBreaksEnvironmentNeutral());
         }
+
+        [Fact]
+        public void SerializeDocWithDollarIdInDollarRefSucceeds()
+        {
+            var expected = @"openapi: '3.1.0'
+info:
+  title: Simple API
+  version: 1.0.0
+paths:
+  /box:
+    get:
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: https://foo.bar/Box
+  /circle:
+    get:
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: https://foo.bar/Circle
+components:
+  schemas:
+    Box:
+      $id: https://foo.bar/Box
+      type: object
+      properties:
+        width:
+          type: number
+        height:
+          type: number
+    Circle:
+      $id: https://foo.bar/Circle
+      type: object
+      properties:
+        radius:
+          type: number
+";
+            var doc = OpenApiDocument.Load("Models/Samples/docWithDollarId.yaml").OpenApiDocument;
+
+            var actual = doc.SerializeAsYaml(OpenApiSpecVersion.OpenApi3_1);
+            actual.MakeLineBreaksEnvironmentNeutral().Should().BeEquivalentTo(expected.MakeLineBreaksEnvironmentNeutral());
+        }
     }
 }

test/Microsoft.OpenApi.Tests/Models/Samples/docWithDollarId.yaml

@@ -0,0 +1,39 @@
+openapi: 3.1.0
+info:
+  title: Simple API
+  version: 1.0.0
+paths:
+  /box:
+    get:
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: https://foo.bar/Box
+  /circle:
+    get:
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: https://foo.bar/Circle
+components:
+  schemas:
+    Box:
+      $id: https://foo.bar/Box
+      type: object
+      properties:
+        width:
+          type: number
+        height:
+          type: number
+    Circle:
+      $id: https://foo.bar/Circle
+      type: object
+      properties:
+        radius:
+          type: number