Well, Visual Studio can create wrappers around your own classes for unit testing purposes. This is called shadow classes or shadow assemblies. This can be used to do the same for framework classes.
There are several steps:
framework.accessor, , , ( ). :
System.dll
.csproj :
<ItemGroup>
<Shadow Include="framework.accessor" />
</ItemGroup>
. , * _Accessor.
( ).
, - , , .