The unified test runner should be split into 2 parts:

1. The common part that is responsible for test running based on the provided json document.
2. The particular unified test file loader that should call the common part.

The initial implementation of this is done here:  https://github.com/DmitryLukyanov/mongo-csharp-driver/blob/csharp3341_history/tests/MongoDB.Driver.Tests/Specifications/unified-test-format/UnifiedTestFormatTestRunner.cs#L31