Add test coverage for collections of self-referential schemas (#60402)

Author: captainsafia

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Transformers/Implementations/OpenApiSchemaReferenceTransformerTests.cs

@@ -628,6 +628,58 @@ await VerifyOpenApiDocument(builder, document =>
         });
     }
 
+    [Fact]
+    public async Task SupportsListOfNestedSchemasWithSelfReference()
+    {
+        // Arrange
+        var builder = CreateBuilder();
+
+        builder.MapPost("/list", (List<LocationContainer> items) => { });
+        builder.MapPost("/array", (LocationContainer[] items) => { });
+        builder.MapPost("/dictionary", (Dictionary<string, LocationContainer> items) => { });
+        builder.MapPost("/", (LocationContainer item) => { });
+
+        await VerifyOpenApiDocument(builder, document =>
+        {
+            var listOperation = document.Paths["/list"].Operations[OperationType.Post];
+            var listRequestSchema = listOperation.RequestBody.Content["application/json"].Schema;
+
+            var arrayOperation = document.Paths["/array"].Operations[OperationType.Post];
+            var arrayRequestSchema = arrayOperation.RequestBody.Content["application/json"].Schema;
+
+            var dictionaryOperation = document.Paths["/dictionary"].Operations[OperationType.Post];
+            var dictionaryRequestSchema = dictionaryOperation.RequestBody.Content["application/json"].Schema;
+
+            var operation = document.Paths["/"].Operations[OperationType.Post];
+            var requestSchema = operation.RequestBody.Content["application/json"].Schema;
+
+            // Assert $ref used for top-level
+            Assert.Equal("LocationContainer", ((OpenApiSchemaReference)listRequestSchema.Items).Reference.Id);
+            Assert.Equal("LocationContainer", ((OpenApiSchemaReference)arrayRequestSchema.Items).Reference.Id);
+            Assert.Equal("LocationContainer", ((OpenApiSchemaReference)dictionaryRequestSchema.AdditionalProperties).Reference.Id);
+            Assert.Equal("LocationContainer", ((OpenApiSchemaReference)requestSchema).Reference.Id);
+
+            // Assert that $ref is used for nested LocationDto
+            var locationContainerSchema = requestSchema;
+            Assert.Equal("LocationDto", ((OpenApiSchemaReference)locationContainerSchema.Properties["location"]).Reference.Id);
+
+            // Assert that $ref is used for nested AddressDto
+            var locationSchema = locationContainerSchema.Properties["location"];
+            Assert.Equal("AddressDto", ((OpenApiSchemaReference)locationSchema.Properties["address"]).Reference.Id);
+
+            // Assert that $ref is used for related LocationDto
+            var addressSchema = locationSchema.Properties["address"];
+            Assert.Equal("LocationDto", ((OpenApiSchemaReference)addressSchema.Properties["relatedLocation"]).Reference.Id);
+
+            // Assert that only expected schemas are generated at the top-level
+            Assert.Equal(3, document.Components.Schemas.Count);
+            Assert.Collection(document.Components.Schemas.Keys,
+                key => Assert.Equal("AddressDto", key),
+                key => Assert.Equal("LocationContainer", key),
+                key => Assert.Equal("LocationDto", key));
+        });
+    }
+
     private class Root
     {
         public Item Item1 { get; set; } = null!;