Check tests for initial value propagation

[killenb]

Child of #123

The initial value propagation is connected with the exception handling scheme because the ExceptionHandlingDecorator takes care that no read transfer succeeds until the initial value could be received.

• Extend the tests to check that no value with invalid time stamp is propagated.

• ReadNonBlocking() and ReadLatest() must block until the initial value could be received

• Special scenario works: Only reading fails (simulate with exception dummy)

  • The device can be opened
  • The initialisation sequence runs through (may be empty)
  • Recovery accessors can be written -> The device is opened successfully and reports no error.
  • The first read operation is executed and fails during its transfer. The device goes to error state, but recovers immediately....
  • All reads block until the read exception has been turned off. The first value is valid and has the right content.

• All the tests should also work for transfer groups. They are only used in the TriggerFanOut. In the current implementation this is not working cleanly yet. Come up with a test scenario and comment it out. Note in the implementation ticket (FIXME does not exist yet) that the test should be activated.

[killenb]

This ticket seem a bit outdated since we have the systematic tests in #179. I see it as an addition to review #179 and check that all special cases mentioned here are covered.

[mhier]

Closed in favour of #179