public abstract class BaseCollectionFixture : ICollectionFixture
    where TFixture : class
{

    protected BaseCollectionFixture(Assembly assemblyUnderTest)
    {
        // Do my fixture stuff with the assembly
    }
}


[CollectionDefinition("Special tests")
public class ConcreteFixture : BaseCollectionFixture
{
    public ConcreteFixture() : base(typeof(MyClassUnderTest).Assembly) {}
}