anchor.diff:  
     nativeBuildInputs = [ cmake ]
      ++ stdenv.lib.optional stdenv.isDarwin fixDarwinDylibNames;
  +  buildInputs = [ bash ];
   
     patches = [
       ./playtests-darwin.patch
  
positive.code:   doCheck = true;
    checkPhase = ''
      runHook preCheck
      ctest -R playTests # The only relatively fast test.
      runHook postCheck
    '';
  
negative.code:     # work fine, and I'm not sure how to write the condition.
      ++ stdenv.lib.optional stdenv.hostPlatform.isWindows ./mcfgthreads-no-pthread.patch;
  
    postPatch = stdenv.lib.optionalString (!static) ''
      substituteInPlace build/cmake/CMakeLists.txt \
        --replace 'message(SEND_ERROR "You need to build static library to build tests")' ""
      substituteInPlace build/cmake/tests/CMakeLists.txt \
  