code: function deltaDebugFiles(file) {
          try {
              logging.increaseIndentation();
              state.fileUnderTest = file;
              logging.logTargetChange(file, state.tmpDir);
  
              // try removing fileUnderTest completely
              var backup = makeBackupFileName();
              fs.renameSync(file, backup);
              if (options.predicate.test(state.mainFileTmpDir)) {
                  return true;
              } else {
                  // if that fails, then restore the fileUnderTest
                  fs.renameSync(backup, file);
                  if (fs.statSync(file).isDirectory()) {
                      var performedAtLeastOneReduction = false;
                      readDirSorted(file).forEach(function (child) {
                          // recurse on all files in the directory
                          performedAtLeastOneReduction |= deltaDebugFiles(child);
                      });
                      return performedAtLeastOneReduction;
                  } else {
                      // specialized reductions
                      if (isJsOrJsonFile(file)) {
                          return delta_single.reduce(makeOptionsForSingleFileMode(file));
                      }
                      return false;
                  }
              }
          } finally {
              logging.decreaseIndentation();
          }
      }
docs: Recursively pass through the file-hierarchy and invoke delta_single.main on all files
  
  @return boolean true if at least one reduction was performed successfully.