Update test file and test

Author: irvinesunday

test/Microsoft.OpenApi.Readers.Tests/V2Tests/OpenApiDocumentTests.cs

@@ -165,6 +165,7 @@ public void ShouldAssignSchemaToAllResponses()
                     .Properties(("id", new JsonSchemaBuilder().Type(SchemaValueType.String).Description("Item identifier."))));
 
             var errorSchema = new JsonSchemaBuilder()
+                    .Ref("#/definitions/Error")
                     .Properties(("code", new JsonSchemaBuilder().Type(SchemaValueType.Integer).Format("int32")),
                         ("message", new JsonSchemaBuilder().Type(SchemaValueType.String)),
                         ("fields", new JsonSchemaBuilder().Type(SchemaValueType.String)));

test/Microsoft.OpenApi.Tests/Models/References/OpenApiResponseReferenceTest.cs

@@ -56,6 +56,12 @@ public class OpenApiResponseReferenceTest
         text/plain:
           schema:
             $ref: '#/components/schemas/Pong'
+  schemas:
+    Pong:
+      type: object
+      properties:
+        sound:
+          type: string
 ";
 
         private readonly OpenApiResponseReference _localResponseReference;