Add unit tests

Add two basic unit tests and a fast path for when the components are registered.

Author: martincostello

src/Microsoft.OpenApi/Validations/Rules/OpenApiDocumentRules.cs

@@ -80,6 +80,12 @@ public override void Visit(IOpenApiSchema schema)
 
             private void ValidateSchemaReference(OpenApiSchemaReference reference)
             {
+                if (reference.RecursiveTarget is not null)
+                {
+                    // The reference was followed to a valid schema somewhere in the document
+                    return;
+                }
+
                 var id = reference.Reference.ReferenceV3;
 
                 if (id is { Length: > 0 } && !IsValidSchemaReference(id, document))

test/Microsoft.OpenApi.Tests/Validations/OpenApiDocumentValidationTests.cs

@@ -0,0 +1,134 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license.
+
+using System.Collections.Generic;
+using System.Linq;
+using System.Net.Http;
+using Xunit;
+
+namespace Microsoft.OpenApi.Validations.Tests;
+
+public static class OpenApiDocumentValidationTests
+{
+    [Fact]
+    public static void ValidateSchemaReferencesAreValid()
+    {
+        // Arrange
+        var document = new OpenApiDocument
+        {
+            Components = new OpenApiComponents(),
+            Info = new OpenApiInfo
+            {
+                Title = "People Document",
+                Version = "1.0.0"
+            },
+            Paths = [],
+            Workspace = new()
+        };
+
+        document.AddComponent("Person", new OpenApiSchema
+        {
+            Type = JsonSchemaType.Object,
+            Properties = new Dictionary<string, IOpenApiSchema>()
+            {
+                ["name"] = new OpenApiSchema { Type = JsonSchemaType.String },
+                ["email"] = new OpenApiSchema { Type = JsonSchemaType.String, Format = "email" }
+            }
+        });
+
+        document.Paths.Add("/people", new OpenApiPathItem
+        {
+            Operations = new Dictionary<HttpMethod, OpenApiOperation>()
+            {
+                [HttpMethod.Get] = new OpenApiOperation
+                {
+                    Responses = new()
+                    {
+                        ["200"] = new OpenApiResponse
+                        {
+                            Description = "OK",
+                            Content = new Dictionary<string, OpenApiMediaType>()
+                            {
+                                ["application/json"] = new OpenApiMediaType
+                                {
+                                    Schema = new OpenApiSchemaReference("Person", document),
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        });
+
+        // Act
+        var errors = document.Validate(ValidationRuleSet.GetDefaultRuleSet());
+        var result = !errors.Any();
+
+        // Assert
+        Assert.True(result);
+        Assert.NotNull(errors);
+        Assert.Empty(errors);
+    }
+
+    [Fact]
+    public static void ValidateSchemaReferencesAreInvalid()
+    {
+        // Arrange
+        var document = new OpenApiDocument
+        {
+            Components = new OpenApiComponents(),
+            Info = new OpenApiInfo
+            {
+                Title = "Pets Document",
+                Version = "1.0.0"
+            },
+            Paths = [],
+            Workspace = new()
+        };
+
+        document.AddComponent("Person", new OpenApiSchema
+        {
+            Type = JsonSchemaType.Object,
+            Properties = new Dictionary<string, IOpenApiSchema>()
+            {
+                ["name"] = new OpenApiSchema { Type = JsonSchemaType.String },
+                ["email"] = new OpenApiSchema { Type = JsonSchemaType.String, Format = "email" }
+            }
+        });
+
+        document.Paths.Add("/pets", new OpenApiPathItem
+        {
+            Operations = new Dictionary<HttpMethod, OpenApiOperation>()
+            {
+                [HttpMethod.Get] = new OpenApiOperation
+                {
+                    Responses = new()
+                    {
+                        ["200"] = new OpenApiResponse
+                        {
+                            Description = "OK",
+                            Content = new Dictionary<string, OpenApiMediaType>()
+                            {
+                                ["application/json"] = new OpenApiMediaType
+                                {
+                                    Schema = new OpenApiSchemaReference("Pet", document),
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        });
+
+        // Act
+        var errors = document.Validate(ValidationRuleSet.GetDefaultRuleSet());
+        var result = !errors.Any();
+
+        // Assert
+        Assert.False(result);
+        Assert.NotNull(errors);
+        var error = Assert.Single(errors);
+        Assert.Equal("The schema reference '#/components/schemas/Pet' does not point to an existing schema.", error.Message);
+        Assert.Equal("#/paths/~1pets/get/responses/200/content/application~1json/schema", error.Pointer);
+    }
+}