Created Unassigned: Unit Test not possible due to Lib [12473]

In a project where i am using the TaskScheduler Lib i cannot create an Unit test becuase of the CS0433 error

The type <type> exists in both DLLs

This is because i need to fake the System.dll but cannot, because your lib is implementing the IReadOnlyCollection and IReadOnlyList with the same namespace..

Is there any way to fix this issue?