  Fluctuation theorems impose constraints on the probability of observing
negative entropy production in small systems driven out of equilibrium. The
range of validity of fluctuation theorems has been extensively tested for
transitions between equilibrium and non equilibrium stationary states, but not
between general non equilibrium states. Here we report an experimental
verification of the detailed fluctuation theorem for the total amount of
entropy produced in the isothermal transition between two non-equilibrium
states. The experimental setup is a parallel $RC$ circuit driven by an
alternating current. We investigate the statistics of the heat released, of the
variation of the entropy of the system, and of the entropy produced for
processes of different durations. We show that the fluctuation theorem is
satisfied with high accuracy for current drivings at different frequencies and
different amplitudes.
