iox-#208: add unit tests for operator+
iox-#208: add unit tests for operator+

Signed-off-by: Marika Lehmann <010fe2c7ccd2af89b5a928b8d30deb5fcfa9e9a5@de.bosch.com>

eclipse-iceoryx/iceoryx,eclipse-iceoryx/iceoryx,eclipse-iceoryx/iceoryx,eclipse-iceoryx/iceoryx