|Subject: ClassCastException in JUnit integration tests
||Author: Robert Lechner
||Date: Fri, 19 June 2015 08:26
We switched our remote services from RMI to ECF and now we get strange errors in JUnit tests.
We are using JUnit for integration tests. That means we start client and server code inside the unit test and run the full business logic there. We also use "real" remote services; that means we call ECF in a way that we get a remote proxy and do a remote call, the same way as if the server would run in a separate JVM. This gives us the possibility to find serialization problems.
It also happens very often that the implementation of a remote service calls another remote service. And now we come to the problem.
Our integration tests (a few thousands) are grouped into about 100 tests suits. Every tests suite is executed in its own JVM, so they don't have any side effects on each other.
In almost every run of the whole package, one ore two suites are failing with the same problem: the call of a remote service fails with an java.lang.ClassCastException. I attached the complete stack trace of such an exception.
It is non-deterministic, which suite or test is failing and which service is called.
Only a small number of tests are failing with this problem (about 1%).
But the problem is always the same: the return type of the method is A, but the return object is of type B. So we get "B cannot be cast to A". The question is: where does the object of type B come from?
Another observation is, that the problem occurs, if one remote service calls another one.
Is it possible that the problem occurs because of the fact that we do remote calls, but caller and callee are in the same JVM?
I wrote special unit tests to reproduce the problem, but was not able to do so.
Do you have an idea where the problem could be located? What is a good place to take a look? I could wrap a dynamic proxy around the ECF proxy to log more information, when the exception is thrown. Because of the high number of tests, I would get a result after a short time.
Any help is appreciated.
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