Stubs as Parameterized Models with Contracts

This is a cool new feature that builds on Stubs, Pex and Code Contracts (in fact, it is really just a consequence of the interaction of the 3 technologies): stubs that act as parameterized models while complying to the interface contracts.

• Code Contracts provide contracts for interfaces. All implementations of that particular interface will be instrumented with the runtime checks by the rewriter at compile time.
• Stubs is really just a code generator that provides a minimal implementation of interfaces and relies on the C# compiler to build the code. Therefore, if a stub implements an interface with contracts, it will automatically be instrumented by the runtime rewriter as well.
• Pex choices (i.e. dynamic parameter generation) may be used as the fallback behavior of stubs. In other words, whenever a stubbed method without user-defined behavior is called, Pex gets to pick the return value. Since the stub implementation itself may have been instrumented with contracts, we’ve added special handling code so that post-condition violation coming from a stub are considered as an assumption. This effectively forces Pex to generate values that comply with the interface contracts.