What's the best way to store cream cheese icing to make it last as long as possible?  How long will it be good for?  The icing is made up of   1/2 cup of butter 1 cup cream cheese 3 cups icing sugar  
The standard test for eggs is to slowly lower your egg(s) in cold water.  If it floats, throw it out.  The smell test will only identify severely rotten eggs, while the float test will hint at how well the egg will perform as a binder in baking recipes.  If it helps, the FDA standard best-by dates are normally 1 week prior to the use-by (which is the date the food is considered no longer fit to use).  The standard use-by date for eggs in the US is 28 days after being laid. After 28 days the chances of bacterial growth within the egg are significant enough that they're not worth using. 