Code review comment for lp://qastaging/~mir-team/mir/port-uncooperative-tests-to-surface-spec

$ bin/mir_unit_tests --gtest_filter=MirProtobufRpcChannelTest.*
Running main() from command_line_server_configuration.cpp
Note: Google Test filter = MirProtobufRpcChannelTest.*
[==========] Running 8 tests from 1 test case.
[----------] Global test environment set-up.
[----------] 8 tests from MirProtobufRpcChannelTest
[ RUN ] MirProtobufRpcChannelTest.ReadsFullMessages
[ OK ] MirProtobufRpcChannelTest.ReadsFullMessages (0 ms)
[ RUN ] MirProtobufRpcChannelTest.ReadsAllQueuedMessages
[ OK ] MirProtobufRpcChannelTest.ReadsAllQueuedMessages (0 ms)
[ RUN ] MirProtobufRpcChannelTest.SendsMessagesAtomically
[ OK ] MirProtobufRpcChannelTest.SendsMessagesAtomically (1 ms)
[ RUN ] MirProtobufRpcChannelTest.SetsCorrectSizeWhenSendingMessage
[ OK ] MirProtobufRpcChannelTest.SetsCorrectSizeWhenSendingMessage (0 ms)
[ RUN ] MirProtobufRpcChannelTest.ReadsFds
[ OK ] MirProtobufRpcChannelTest.ReadsFds (1 ms)
[ RUN ] MirProtobufRpcChannelTest.NotifiesOfDisconnectOnWriteError
/home/alan/display_server/mir4/tests/unit-tests/client/test_protobuf_rpc_channel.cpp:321: Failure
Expected: channel_user.exchange_buffer(nullptr, &request, &reply, google::protobuf::NewCallback([](){})) throws an exception of type std::runtime_error.
  Actual: it throws nothing.
[ FAILED ] MirProtobufRpcChannelTest.NotifiesOfDisconnectOnWriteError (0 ms)
[ RUN ] MirProtobufRpcChannelTest.ForwardsDisconnectNotification
[ OK ] MirProtobufRpcChannelTest.ForwardsDisconnectNotification (0 ms)
[ RUN ] MirProtobufRpcChannelTest.NotifiesOfDisconnectOnlyOnce
/home/alan/display_server/mir4/tests/unit-tests/client/test_protobuf_rpc_channel.cpp:382: Failure
Expected: channel_user.exchange_buffer(nullptr, &request, &reply, google::protobuf::NewCallback([](){})) throws an exception of type std::runtime_error.
  Actual: it throws nothing.
[ FAILED ] MirProtobufRpcChannelTest.NotifiesOfDisconnectOnlyOnce (1 ms)
[----------] 8 tests from MirProtobufRpcChannelTest (3 ms total)

[----------] Global test environment tear-down
[==========] 8 tests from 1 test case ran. (4 ms total)
[ PASSED ] 6 tests.
[ FAILED ] 2 tests, listed below:
[ FAILED ] MirProtobufRpcChannelTest.NotifiesOfDisconnectOnWriteError
[ FAILED ] MirProtobufRpcChannelTest.NotifiesOfDisconnectOnlyOnce

 2 FAILED TESTS