diff --git a/tests/forces/Test_fthmc.cc b/tests/forces/Test_fthmc.cc
new file mode 100644
index 00000000..0a64cdb9
--- /dev/null
+++ b/tests/forces/Test_fthmc.cc
@@ -0,0 +1,170 @@
+/*************************************************************************************
+
+    Grid physics library, www.github.com/paboyle/Grid 
+
+    Source file: ./tests/Test_fthmc.cc
+
+    Copyright (C) 2022
+
+Author: Peter Boyle <pboyle@bnl.gov>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with this program; if not, write to the Free Software Foundation, Inc.,
+    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+    See the full license in the file "LICENSE" in the top level distribution directory
+    *************************************************************************************/
+    /*  END LEGAL */
+#include <Grid/Grid.h>
+#include <Grid/qcd/smearing/GaugeConfigurationMasked.h>
+#include <Grid/qcd/smearing/JacobianAction.h>
+
+using namespace std;
+using namespace Grid;
+
+
+template<class Gimpl>
+void ForceTest(Action<LatticeGaugeField> &action,SmearedConfigurationMasked<PeriodicGimplR> & smU,MomentumFilterBase<LatticeGaugeField> &Filter)
+{
+  LatticeGaugeField U = smU.get_U(false); // unsmeared config
+  GridBase *UGrid = U.Grid();
+
+  std::vector<int> seeds({1,2,3,5});
+  GridSerialRNG            sRNG;         sRNG.SeedFixedIntegers(seeds);
+  GridParallelRNG          RNG4(UGrid);  RNG4.SeedFixedIntegers(seeds);
+
+  LatticeColourMatrix Pmu(UGrid); 
+  LatticeGaugeField P(UGrid); 
+  LatticeGaugeField UdSdU(UGrid); 
+
+  std::cout << GridLogMessage << "*********************************************************"<<std::endl;
+  std::cout << GridLogMessage << " Force test for "<<action.action_name()<<std::endl;
+  std::cout << GridLogMessage << "*********************************************************"<<std::endl;
+  
+  RealD eps=0.005;
+
+  std::cout << GridLogMessage << "+++++++++++++++++++++++++++++++++++++++++++++++++++++++++"<<std::endl;
+  std::cout << GridLogMessage << " Refresh "<<action.action_name()<<std::endl;
+  std::cout << GridLogMessage << "+++++++++++++++++++++++++++++++++++++++++++++++++++++++++"<<std::endl;
+  
+  Gimpl::generate_momenta(P,sRNG,RNG4);
+  Filter.applyFilter(P);
+
+  action.refresh(smU,sRNG,RNG4);
+
+  std::cout << GridLogMessage << "+++++++++++++++++++++++++++++++++++++++++++++++++++++++++"<<std::endl;
+  std::cout << GridLogMessage << " Action "<<action.action_name()<<std::endl;
+  std::cout << GridLogMessage << "+++++++++++++++++++++++++++++++++++++++++++++++++++++++++"<<std::endl;
+
+  RealD S1 = action.S(smU);
+
+  Gimpl::update_field(P,U,eps);
+  smU.set_Field(U);
+
+  std::cout << GridLogMessage << "+++++++++++++++++++++++++++++++++++++++++++++++++++++++++"<<std::endl;
+  std::cout << GridLogMessage << " Derivative "<<action.action_name()<<std::endl;
+  std::cout << GridLogMessage << "+++++++++++++++++++++++++++++++++++++++++++++++++++++++++"<<std::endl;
+  action.deriv(smU,UdSdU);
+  UdSdU = Ta(UdSdU);
+  Filter.applyFilter(UdSdU);
+
+  DumpSliceNorm("Force",UdSdU,Nd-1);
+  
+  Gimpl::update_field(P,U,eps);
+  smU.set_Field(U);
+
+  std::cout << GridLogMessage << "+++++++++++++++++++++++++++++++++++++++++++++++++++++++++"<<std::endl;
+  std::cout << GridLogMessage << " Action "<<action.action_name()<<std::endl;
+  std::cout << GridLogMessage << "+++++++++++++++++++++++++++++++++++++++++++++++++++++++++"<<std::endl;
+  
+  RealD S2 = action.S(smU);
+
+  // Use the derivative
+  LatticeComplex dS(UGrid); dS = Zero();
+  for(int mu=0;mu<Nd;mu++){
+    auto UdSdUmu = PeekIndex<LorentzIndex>(UdSdU,mu);
+    Pmu= PeekIndex<LorentzIndex>(P,mu);
+    dS = dS - trace(Pmu*UdSdUmu)*eps*2.0*2.0;
+  }
+  ComplexD dSpred    = sum(dS);
+  RealD diff =  S2-S1-dSpred.real();
+
+  std::cout<< GridLogMessage << "+++++++++++++++++++++++++++++++++++++++++++++++++++++++++"<<std::endl;
+  std::cout<< GridLogMessage << "S1 : "<< S1    <<std::endl;
+  std::cout<< GridLogMessage << "S2 : "<< S2    <<std::endl;
+  std::cout<< GridLogMessage << "dS : "<< S2-S1 <<std::endl;
+  std::cout<< GridLogMessage << "dSpred : "<< dSpred.real() <<std::endl;
+  std::cout<< GridLogMessage << "diff : "<< diff<<std::endl;
+  std::cout<< GridLogMessage << "*********************************************************"<<std::endl;
+  //  assert(diff<1.0);
+  std::cout<< GridLogMessage << "Done" <<std::endl;
+  std::cout << GridLogMessage << "*********************************************************"<<std::endl;
+}
+
+int main (int argc, char ** argv)
+{
+  Grid_init(&argc,&argv);
+
+  std::cout << std::setprecision(14);
+  Coordinate latt_size   = GridDefaultLatt();
+  Coordinate mpi_layout  = GridDefaultMpi();
+  Coordinate simd_layout = GridDefaultSimd(Nd,vComplex::Nsimd());
+  Coordinate shm;
+  GlobalSharedMemory::GetShmDims(mpi_layout,shm);
+
+  const int Ls=12;
+  const int Nt = latt_size[3];
+  GridCartesian         * UGrid   = SpaceTimeGrid::makeFourDimGrid(GridDefaultLatt(), GridDefaultSimd(Nd,vComplex::Nsimd()),GridDefaultMpi());
+  GridCartesian         * FGrid   = SpaceTimeGrid::makeFiveDimGrid(Ls,UGrid);
+
+  ///////////////////// Gauge Field and Gauge Forces ////////////////////////////
+  LatticeGaugeField U(UGrid);
+
+#if  0
+  FieldMetaData header;
+  std::string file("./ckpoint_lat.2000");
+  NerscIO::readConfiguration(U,header,file);
+#else
+  std::vector<int> seeds({1,2,3,4,5,6,7,8});
+  GridParallelRNG          RNG4(UGrid);  RNG4.SeedFixedIntegers(seeds);
+  SU<Nc>::HotConfiguration(RNG4,U);
+#endif
+
+  
+  RealD beta=6.0;
+  WilsonGaugeActionR  PlaqAction(beta);
+  IwasakiGaugeActionR RectAction(beta);
+
+
+  ////////////////////////////////////////////////
+  // Plaquette only FTHMC smearer
+  ////////////////////////////////////////////////
+  double rho = 0.1;
+  Smear_Stout<PeriodicGimplR> Smearer(rho);
+  SmearedConfigurationMasked<PeriodicGimplR> SmartConfig(UGrid,2*Nd,Smearer,true);
+
+  JacobianAction<PeriodicGimplR> Jacobian(&SmartConfig);
+  
+  ////////////////////////////////////////////////
+  // Run some tests
+  ////////////////////////////////////////////////
+  MomentumFilterNone<LatticeGaugeField> FilterNone;
+  SmartConfig.set_Field(U);
+  ForceTest<GimplTypesR>(PlaqAction,SmartConfig,FilterNone);
+  SmartConfig.set_Field(U);
+  ForceTest<GimplTypesR>(RectAction,SmartConfig,FilterNone);
+  SmartConfig.set_Field(U);
+  ForceTest<GimplTypesR>(Jacobian,SmartConfig,FilterNone);
+
+  Grid_finalize();
+}