add tests for onDataChange to throw exceptions if a non-function is given
add tests for onDataChange to throw exceptions if a non-function is given

AliTVTeam/AliTV,BioInf-Wuerzburg/AliTV,BioInf-Wuerzburg/AliTV,BioInf-Wuerzburg/AliTV,BioInf-Wuerzburg/AliTV,BioInf-Wuerzburg/AliTV,AliTVTeam/AliTV,BioInf-Wuerzburg/AliTV