I am unit testing a StateMachineWorkflow and I create my test methods by clicking in my test project and I make Add - UnitTest. In the project window I select the workflow that I want to test and all the methods in it.
Visual Studio generated a Test Reference folder in my Test Project with an accessor to the workflow. It also generated all the TestMethod() necessary for the testing. All test Methods use a MyWorkflow_Accessor target = new MyWorkflow_Accessor(). When I need to call a function I just do something like target.SendEmail().
Everything works fine, except for one thing: I can't use WorkflowInstanceId of the Workflow, when the code reach a line that uses this it throws an exception in the Workflow, "This is an invalid design time operation. You can only perform the operation at runtime." Is it possible to inject the WorkflowID by code? Is there any workaround to this situation? I use the WorkflowInstanceId in a lot of functions and changing the Workflow code to match my test doesn't seem like a good idea because I believe the problem is in the test and not in the workflow.
It's not clear from your question if you're using WF 3.5 or WF4 with the state machine update. For the latter, you can use Microsoft.Activities.UnitTesting to test workflows.
It sounds like you're using WF 3.5, though. If this is new development, I would seriously consider moving to WF4. Microsoft basically rewrote WF, and the sooner you switch, the easier your migration path will be.
Otherwise, there is some information on testing with WF 3.5 on MSDN.