For a gambler's mindset, why should they undergo a swab test just for the purpose to enter the casino? If I'm a gambler I'd rather find other casinos with no restrictions like that unless I'm a die-hard player of the said casino. It's no different from other establishments wherein there is no need for a test.
Swab test is necessary if your place was in the high virus-infected record, but if the place that has flatten curve record of virus-infected and if they are in a modified general quarantine level, so this is a case to case basis. Thermal testing and proper guidelines for sanitation or disinfectant will be fine.
Though it is risky for gamblers to do this, I guess if they really want to they will find ways just to gamble.
If I remember swab test will take atleast few hours to get the result and it is much expensive test kit needed to do that so it is not actually possible to swab test every person enters into the casino and also social distancing will not be possible in any casinos so government should allow the casinos to work even if they know it will result into spread just for economy gain or they should completely close it.