acceptance-tests.BespokeDisplayServerTestFixture is failing randomly (approx 10% of the time)

acceptance-tests.BespokeDisplayServerTestFixture is failing randomly (approx 10% of the time). This is from the latest lp:mir ...

The following tests FAILED:
   1 - acceptance-tests.BespokeDisplayServerTestFixture.* (Failed)
Errors while running CTest

[ RUN ] BespokeDisplayServerTestFixture.focus_management
unknown file: Failure

Unexpected mock function call - taking default action specified at:
/home/dan/bzr/mir/toy/tests/acceptance-tests/test_focus_management_api.cpp:135:
    Function call: create_surface_for(@0x7ff518000c70 16-byte object <D8-14 00-18 F5-7F 00-00 C0-14 00-18 F5-7F 00-00>, @0x7ff52a4bb410 24-byte object <D8-0A 00-14 F5-7F 00-00 80-02 00-00 E0-01 00-00 01-00 00-00 01-00 00-00>)
          Returns: 0
Google Mock tried the following 1 expectation, but it didn't match:

/home/dan/bzr/mir/toy/tests/acceptance-tests/test_focus_management_api.cpp:174: EXPECT_CALL(*mock_shell, create_surface_for(_,_))...
         Expected: all pre-requisites are satisfied
           Actual: the following immediate pre-requisites are not satisfied:
/home/dan/bzr/mir/toy/tests/acceptance-tests/test_focus_management_api.cpp:173: pre-requisite #0
                   (end of pre-requisites)
         Expected: to be called once
           Actual: never called - unsatisfied and active
unknown file: Failure

Unexpected mock function call - taking default action specified at:
/home/dan/bzr/mir/toy/tests/acceptance-tests/test_focus_management_api.cpp:130:
    Function call: close_session(@0x7ff510000bd0 16-byte object <48-13 00-18 F5-7F 00-00 30-13 00-18 F5-7F 00-00>)
Google Mock tried the following 1 expectation, but it didn't match:

/home/dan/bzr/mir/toy/tests/acceptance-tests/test_focus_management_api.cpp:175: EXPECT_CALL(*mock_shell, close_session(_))...
         Expected: all pre-requisites are satisfied
           Actual: the following immediate pre-requisites are not satisfied:
/home/dan/bzr/mir/toy/tests/acceptance-tests/test_focus_management_api.cpp:174: pre-requisite #0
                   (end of pre-requisites)
         Expected: to be called twice
           Actual: never called - unsatisfied and active
unknown file: Failure

Unexpected mock function call - taking default action specified at:
/home/dan/bzr/mir/toy/tests/acceptance-tests/test_focus_management_api.cpp:130:
    Function call: close_session(@0x7ff518000c70 16-byte object <D8-14 00-18 F5-7F 00-00 C0-14 00-18 F5-7F 00-00>)
Google Mock tried the following 1 expectation, but it didn't match:

/home/dan/bzr/mir/toy/tests/acceptance-tests/test_focus_management_api.cpp:175: EXPECT_CALL(*mock_shell, close_session(_))...
         Expected: all pre-requisites are satisfied
           Actual: the following immediate pre-requisites are not satisfied:
/home/dan/bzr/mir/toy/tests/acceptance-tests/test_focus_management_api.cpp:174: pre-requisite #0
                   (end of pre-requisites)
         Expected: to be called twice
           Actual: never called - unsatisfied and active
unknown file: Failure

Unexpected mock function call - taking default action specified at:
/home/dan/bzr/mir/toy/tests/acceptance-tests/test_focus_management_api.cpp:137:
    Function call: shutdown()
Google Mock tried the following 1 expectation, but it didn't match:

/home/dan/bzr/mir/toy/tests/acceptance-tests/test_focus_management_api.cpp:176: EXPECT_CALL(*mock_shell, shutdown())...
         Expected: all pre-requisites are satisfied
           Actual: the following immediate pre-requisites are not satisfied:
/home/dan/bzr/mir/toy/tests/acceptance-tests/test_focus_management_api.cpp:175: pre-requisite #0
                   (end of pre-requisites)
         Expected: to be called once
           Actual: never called - unsatisfied and active
Google Test trace:
/home/dan/bzr/mir/toy/tests/mir_test_framework/testing_process_manager.cpp:76: Server
/home/dan/bzr/mir/toy/tests/acceptance-tests/test_focus_management_api.cpp:176: Failure
Actual function call count doesn't match EXPECT_CALL(*mock_shell, shutdown())...
         Expected: to be called once
           Actual: never called - unsatisfied and active
Google Test trace:
/home/dan/bzr/mir/toy/tests/mir_test_framework/testing_process_manager.cpp:76: Server
/home/dan/bzr/mir/toy/tests/acceptance-tests/test_focus_management_api.cpp:174: Failure
Actual function call count doesn't match EXPECT_CALL(*mock_shell, create_surface_for(_,_))...
         Expected: to be called once
           Actual: never called - unsatisfied and active
Google Test trace:
/home/dan/bzr/mir/toy/tests/mir_test_framework/testing_process_manager.cpp:76: Server
/home/dan/bzr/mir/toy/tests/acceptance-tests/test_focus_management_api.cpp:175: Failure
Actual function call count doesn't match EXPECT_CALL(*mock_shell, close_session(_))...
         Expected: to be called twice
           Actual: never called - unsatisfied and active
Google Test trace:
/home/dan/bzr/mir/toy/tests/mir_test_framework/testing_process_manager.cpp:76: Server
/home/dan/bzr/mir/toy/tests/mir_test_framework/testing_process_manager.cpp:219: Failure
Value of: result.succeeded()
  Actual: false
Expected: true
process::Result(child_terminated_normally, failure(1))
[ FAILED ] BespokeDisplayServerTestFixture.focus_management (14 ms)