why benzaldehyde do not respond to fehling's test?

Benzaldehyde is a mixture of equal volumes of 2 solutions namely, Fehling solution A and Fehling solution B.

Fehling solution A consists of CuSO4 solution

Fehling solution B consists of NaOH+Roschelle's salt..

Benzaldehyde easily reacts with this NaOH in rochelle's salt instead of reacting with CuSO4 .. Hence Benzaldehyde doesnt react with fehling solution..

Extra: Rochelle's salt is sodium potassium tartate..

structure:    COONa

                    |

             H--- C --OH

                   |

          OH--- C -- H

                   |

                  COOK