I don't think we need to add this validation in the reference resolver itself. In general, we try to avoid adding a validation into the reader and resolver unless we have to (e.g. YAML malformatting can't really be validated anywhere else).

This seems like it would fit better in the Validations Rules

https://github.com/Microsoft/OpenAPI.NET/tree/master/src/Microsoft.OpenApi/Validations/Rules

This rule belongs to OpenApiSchemaRules. #Closed

Okay, I will move the validation into OpenApiSchemaRules. Thanks. #Closed

Thanks for adding the tests to the reader. Could you help move the tests to OpenApiSchemaValidationTests.cs? Also, the tests should be adjusted to simply read the Schema object instead of the real document. #Closed

Thanks for the review. I have moved test cases to OpenApiSchemaValidationTests (with changes) and updated code as per the comments. #Closed

Thank you for making this change. I have left a few minor comments. Once you have fixed that and merged in the latest master, we should be good to go :)

Edit: Looks like merge is not needed given no conflicts. Github wasn't updating correctly for me.

I have updated the resource keys and reverted changes to OpenApiDiscriminatorTests. Thanks again. 👍

This looks good now. I'll check it in.

Thanks a lot for your contribution :)

Thankyou very much