An orchestrator in a Web Service system is a locally deployed piece of software used both to allow users to interact with the system and to communicate with remote components (Web Services) in order to fulfill a goal. We propose a symbolic model based approach to test orchestrators in the context of the systems they pilot. Our approach only takes as input a model of the orchestrator and no models of the Web Services. Besides, the testing architecture is a parameter: communications between Web Services and the orchestrator can be either simulated, or hidden or observable. When they are simulated, the orchestrator is tested in isolation and our approach comes to already defined classical model-based unit testing approaches. When the System Under Test is connected with Web Services (that is, in actual usage) it is no longer fully controlled by the tester, but tested in context In that case two situations may occur: either communications with Web Services are observable or they are hidden. Our approach copes with those cases. We give theorems relating our notion of conformance in context with regard to classical conformance of components in isolation. We present a test case generation algorithm based on symbolic execution techniques: it takes into account the status (controllable, hidden, or observable) of communication channels between the orchestrator and Web Services. The algorithm has been implemented and is illustrated on a small case study