Multiple WCF Services implementing same Service Contract interface

Question

Is it possible for multiple wcf services to implement the same service contract interface?

What I want to do is allow for a test service to be interchangeable for the real service, and to specify which service to be used in the configuration file.

For example:

[ServiceContract]
public interface IUselessService  
{  
  [OperationContract]   
  string GetData(int value);   
}  

Test implementation

public class TestService : IUselessService  
{  
  public string GetData(int value)  
  {  
    return "This is a test";   
  }  
}  

Real class

public class RealService : IUselessService  
{  
  public string GetData(int value)  
  {  
    return string.Format("You entered: {0}", value);  
  }  
}

Answer 1

Yes, it's not only possible, it is explicitly within the design intentions of service contract interfaces.

Answer 2

Thanks guys for your answers. I have a solution now that works for me, without putting the interface in a separate assembly and in the GAC. I'm not looking at using the interface for other projects, just using the same interface for multiple services in the same project.

What I was trying to do was make the change between RealService and TestService in the configuration file of the WCF service, so the client would not know the difference (the client would not have to change its configuration to point to a different .svc file). I'm not sure this is possible, or it least if it is, it is definitely not straightfoward.

What I am doing now is just specifying both services in the configuration file of the WCF service, and then I point the client to one or the other based on which service I want. Since this WCF service is for internal use only and we have control of both the client and the service, it is not a bad tradeoff. This solution is probably more explicit in its intentions anyways.

Here is the snippet of the configuration file:

<services>
      <service behaviorConfiguration="WcfService1.Service1Behavior"
               name="WcfService1.TestService">
        <endpoint address="" binding="basicHttpBinding" bindingConfiguration="testBasicHttpBinding" 
          contract="WcfService1.IUselessService">              
        </endpoint>
        <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange" />
      </service>
      <service behaviorConfiguration="WcfService1.Service1Behavior"
               name="WcfService1.RealService">
        <endpoint address="" binding="basicHttpBinding" bindingConfiguration="testBasicHttpBinding"
         contract="WcfService1.IUselessService">             
        </endpoint>
        <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange" />
      </service>
    </services>