Fixed thrown exceptions

Author: darrelmiller

src/Microsoft.OpenApi.Readers/V2/OpenApiV2VersionService.cs

@@ -7,6 +7,7 @@
 using Microsoft.OpenApi.Exceptions;
 using Microsoft.OpenApi.Interfaces;
 using Microsoft.OpenApi.Models;
+using Microsoft.OpenApi.Readers.Exceptions;
 using Microsoft.OpenApi.Readers.Interface;
 using Microsoft.OpenApi.Readers.ParseNodes;
 using Microsoft.OpenApi.Readers.Properties;
@@ -90,7 +91,7 @@ private static ReferenceType ParseReferenceType(string referenceTypeName)
                     return ReferenceType.SecurityScheme;
 
                 default:
-                    throw new ArgumentException();
+                    throw new OpenApiReaderException($"Unknown reference type '{referenceTypeName}'");
             }
         }
 

src/Microsoft.OpenApi/Models/OpenApiDocument.cs

@@ -305,6 +305,10 @@ public IOpenApiReferenceable ResolveReference(OpenApiReference reference)
                 return null;
             }
 
+            if (this.Components == null) {
+                throw new OpenApiException(string.Format(Properties.SRResource.InvalidReferenceId, reference.Id));
+            }
+
             try
             {
                 switch (reference.Type)

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

@@ -0,0 +1,77 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using FluentAssertions;
+using Microsoft.OpenApi.Exceptions;
+using Microsoft.OpenApi.Models;
+using Microsoft.OpenApi.Readers.Exceptions;
+using Xunit;
+
+namespace Microsoft.OpenApi.Readers.Tests.V2Tests
+{
+    public class OpenApiDocumentTests
+    {
+        [Fact]
+        public void ShouldThrowWhenReferenceTypeIsInvalid()
+        {
+            var input = @"
+swagger: 2.0
+info: 
+  title: test
+  version: 1.0.0
+paths: 
+  '/':
+    get:
+      responses:
+        '200':
+          description: ok
+          schema:
+            $ref: '#/definition/does/notexist'
+";
+
+            var reader = new OpenApiStringReader(new OpenApiReaderSettings() {
+            });
+
+            OpenApiDocument doc = null;
+
+            Assert.Throws<OpenApiReaderException>(() =>
+            doc = reader.Read(input, out var diagnostic));
+
+            Assert.Null(doc);
+        }
+
+
+        [Fact]
+        public void ShouldThrowWhenReferenceDoesNotExist()
+        {
+            var input = @"
+swagger: 2.0
+info: 
+  title: test
+  version: 1.0.0
+paths: 
+  '/':
+    get:
+      produces: ['application/json']
+      responses:
+        '200':
+          description: ok
+          schema:
+            $ref: '#/definitions/doesnotexist'
+";
+
+            var reader = new OpenApiStringReader(new OpenApiReaderSettings()
+            {
+            });
+
+            OpenApiDocument doc = null;
+
+            doc = reader.Read(input, out var diagnostic);
+
+            diagnostic.Errors.ShouldBeEquivalentTo(new List<OpenApiError> {
+                new OpenApiError( new OpenApiException("Invalid Reference identifier 'doesnotexist'.")) });
+        }
+    }
+}

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

@@ -2496,5 +2496,60 @@ public void SerializeSimpleDocumentWithTopLevelSelfReferencingWithOtherPropertie
             expected = expected.MakeLineBreaksEnvironmentNeutral();
             actual.Should().Be(expected);
         }
+
+        [Fact]
+        public void SerializeDocumentWithReferenceButNoComponents()
+        {
+            // Arrange
+            var document = new OpenApiDocument()
+            {
+                Info = new OpenApiInfo
+                {
+                    Title = "Test",
+                    Version = "1.0.0"
+                },
+                Paths = new OpenApiPaths
+                {
+                    ["/"] = new OpenApiPathItem
+                    {
+                        Operations = new Dictionary<OperationType, OpenApiOperation>
+                        {
+                            [OperationType.Get] = new OpenApiOperation
+                            {
+                                Responses = new OpenApiResponses
+                                {
+                                    ["200"] = new OpenApiResponse
+                                    {
+                                        Content = new Dictionary<string, OpenApiMediaType>()
+                                        {
+                                            ["application/json"] = new OpenApiMediaType
+                                            {
+                                                Schema = new OpenApiSchema
+                                                {
+                                                    Reference = new OpenApiReference
+                                                    {
+                                                        Id = "test",
+                                                        Type = ReferenceType.Schema
+                                                    }
+                                                }
+                                            }
+                                        }
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            };
+
+
+            var reference = document.Paths["/"].Operations[OperationType.Get].Responses["200"].Content["application/json"].Schema.Reference;
+
+            // Act
+            var actual = document.Serialize(OpenApiSpecVersion.OpenApi2_0, OpenApiFormat.Json);
+
+            // Assert
+            Assert.NotEmpty(actual);
+        }
     }
 }