What is the best way to determine if an aqueous solution of sodium nitrate is unsaturated

Solution is said to be saturated, if it contains maximum amount of solute that it can hold.  On other hand, if solution contains less amount of solute as compared to its maximum capacity, it is referred as unsaturated solution.

It may be noted that, solubility of system is depends on temperature. 

Now, if solution is unsaturated then it will dissolve more solute, when added in it. Thus,  sodium nitrate when added to solution get dissolves, it suggest that solution is unsaturated. 

Any photo? or something