FakeTransaction | Make us a BitCoin client | Cryptocurrency library

I think the real problem is that fakeTransaction isn't the same object inside the SM.Run call as it is in the test. What class is it exactly? We don't have the definition of fakeTransaction up above, but I see that you send a serialized representation of it into the request, not the original object.

So SM.Run eventually calls fakeService.RetrieveBatch(Transaction session) with a reconstituted session object. What are the equality semantics of the Transaction class? The configured Fake's RetrieveBatch method will, as described in argument constraints, compare its input with fakeTransaction using object.Equals, and if it does not match, your configured behaviour will not be triggered.

If you're unsure about the equality semantics of Transaction, consider reconstituting transaction from the byte array right in your test, and running object.Equals on the two objects. That will show you whether they compare as equal.

If Transaction turns out not to have value-based equality semantics, you will likely have to use one of the other argument constraint mechanisms, such as a custom matcher that examines the transaction's properties or maybe even ignore the actual value using A.Ignored.