twisted.test.test_process.TestProcessProtocol reports failures poorly

[exarkun]

TestProcessProtocol.childConnectionLost expects "1234" exactly to be written to stderr by the time it runs. If it is not, then it prints a message and raises a RuntimeError. This will eventually cause the test running to timeout and fail, which is better than nothing, but the error should be reported in a much better way that causes a sensible failure report to happen immediately.