Solution structuring and TDD in Visual Studio

I'm currently working on solution structuring for a large system using TDD. To be able to work efficiently within the project we have defined a set of solution types with different purposes. This is the setup we ended up with:

Workbench
TDD requires that the solutions you spend most of your time in builds as fast as possible. To achieve this you have to keep the project number within the solution to a minimum. If you cannot get arround having multiple dependencies for every project, binary references would be the way to go. We have choosen a more decoupled approach where every project depends upon abstractions and interfaces are wired to implementations through a DI container. Contracts and interfaces are separated out into contract projects. This keeps project references down to just referencing interface/contracts projects. The build output from this solution would not be able to run since the contract implementations are not referenced here. The solution contains all environment independent unit and integration tests for this workbench's projects. Because of practicing TDD it's not important that the solution is able to run but that the tests are able to pass. A workbench exists for every bounded context and standalone code library.

Test rig
Even though most of our time is spent writing tests and code in the workbench solutions we some times have the need to debug a running system. These solutions contain all code needed to run parts of the system like hosting services or even complete running systems. The test rig solutions are usually quite large and takes time to build but, theire there for us to ocasionally test the system locally.

Continous Integration solution
This solution contains all projects and  all environment independent unit and integration test for the complete system. This solution is part of the continous integration build performed on check in. Naturally CI runs all tests on every build.

System test solution
We need a solution containing environment dependent tests requiring things like database access or a running system.The tests within this solution should run on every deployment to the test environment to make sure the system wiring is intact.

As for deployment both test rigs and continous integration solutions contains enough of the system to be able to perform deployment.

It would really be interresting to see how other people are working on similar projects.