How to Create a XUnit Mock Unit test cases in .net core for IOktaClient

How to Create a XUnit Mock Unit test cases in .net core application, When i checked with internet i found the below reference, but in this they are not using mock for IOktaClient, instead they are using some test environments.

Reference: okta-sdk-dotnet/TestClient.cs at master · okta/okta-sdk-dotnet · GitHub

Please guide me how to create a Mock Object for IOktaClient.

Thanks,
PRakash Kumar