anchor.diff:          dalton = callPackage ./tests/dalton { };
           hpcg = callPackage ./tests/hpcg { };
           hpl = callPackage ./tests/hpl { };
  -        mesa-qc = callPackage ./tests/mesa { };
  +        mesa-qc = nullable mesa-qc (callPackage ./tests/mesa { });
           molcas = callPackage ./tests/molcas { };
           #molcasUnstable = callPackage ./tests/molcas { molcas=self.molcasUnstable; };
  -        mrcc = callPackage ./tests/mrcc { };
  +        mrcc = nullable mrcc (callPackage ./tests/mrcc { });
           nwchem = callPackage ./tests/nwchem { };
           psi4 = callPackage ./tests/psi4 { };
  -        qdng = callPackage ./tests/qdng { };
  +        qdng = nullable qdng (callPackage ./tests/qdng { });
           dgemm = callPackage ./tests/dgemm { };
           stream = callPackage ./tests/stream { };
  -        turbomole = callPackage ./tests/turbomole { };
  +        turbomole = nullable turbomole (callPackage ./tests/turbomole { });
           xtb = callPackage ./tests/xtb { };
         }  // lib.optionalAttrs (cfg.licMolpro != null) {
           molpro = callPackage ./tests/molpro { };
  
positive.code: 
        bagel-serial = callPackage ./bagel { mpi = null; blas = self.mkl; };
  
        cefine = callPackage ./cefine { };
  
        cfour = callPackage ./cfour { };
  
  
negative.code: 
        f2c = callPackage ./f2c { };
  
        tests = with self; {
          cfour = callPackage ./tests/cfour { };
          cp2k = callPackage ./tests/cp2k { };
          bagel = callPackage ./tests/bagel { };
  