anchor.diff:      snapshot = '$tmp/snapshot';
       env = Map<String, String>.from(e);
       env['DART_CONFIGURATION'] = tag;
  -    cmd = [precompiler] + extraFlags + [fileName, snapshot];
  +    cmd = [precompiler, ...extraFlags, fileName, snapshot];
     }
   
     TestResult run() {
  
positive.code:       this.fileName, List<String> extraFlags) {
      description = '$prefix-$tag';
      dart = '$top/out/$tag/dart';
      cmd = [dart] + extraFlags + [fileName];
    }
  
    TestResult run() {
  
negative.code: /// Command runner.
  TestResult runCommand(List<String> cmd, Map<String, String> env) {
    ProcessResult res = Process.runSync(
        'timeout', ['-s', '$sigkill', '$timeout', ...cmd],
        environment: env);
    if (debug) {
      print('\nrunning $cmd yields:\n'
  