anchor.diff:    await d.file('pubspec.yaml', r'''
   name: peanut_test
   
  +environment:
  +  sdk: '>=2.10.0 <3.0.0'
  +
   dev_dependencies:
     build_runner: '>=0.8.10 <2.0.0'
     build_web_compilers: '>=1.0.0 <3.0.0'
  
positive.code: }
  
  Future<void> _pubGet({String parent}) async {
    final proc = await Process.run('pub', ['get', '--offline', '--no-precompile'],
        workingDirectory: p.join(d.sandbox, parent));
    expect(proc.exitCode, 0,
        reason: [
          'STDOUT:',
          proc.stdout as String,
          'STDERR:',
          proc.stderr as String,
        ].map((str) => str.trim()).join('\n'));
  }
  
  Future<GitDir> _initGitDir() async {
  
negative.code:   }
  }
  
  final _exampleFiles = Map.fromEntries(
    Directory('example')
        .listSync()
        .cast<File>()
        .map((f) => MapEntry(p.basename(f.path), f.readAsStringSync())),
  );
  
  Future _logGitTree(GitDir gitDir, String sha, {int depth = 0}) async {
    final treeContents = await gitDir.lsTree(sha);
  