create a minimal test that produces an optimistic locking failure.

I believe the simplest way to test this is something like this:

Start a process instance with 2 wait states and put it in the first wait state.

EnvironmentFactory environmentFactory = get it from some configuration file

Environment environment1 = environmentFactory.openEnvironment();
Session session1 = environment1.get(Session.class);
ExecutionImpl processInstance1 = session1.load(ExecutionImpl.class, processInstanceDbid);

Environment environment2 = environmentFactory.openEnvironment();
Session session2 = environment2.get(Session.class);
ExecutionImpl processInstance2 = session2.load(ExecutionImpl.class, processInstanceDbid);

processInstance1.signal();
processInstance2.signal();

environment2.close();
environment1.close();