The Fehling test involves two reagents: a clear blue solution containing copper sulphate and a colorless solution containing sodium tartrate.
Add both solutions to the sugar and place the entire mixture in boiling water.
If the sugar is reducing, a brick red precipitate forms.
On adding sucrose or another non-reducing sugar, the mixture stays clear blue.
Sucrose does not react with Fehling's reagent because Sucrose is not a reducing sugar.