diff --git a/packages/cutler/FORKING_FLUTTER.md b/packages/cutler/FORKING_FLUTTER.md
index a44447c9..8c632f20 100644
--- a/packages/cutler/FORKING_FLUTTER.md
+++ b/packages/cutler/FORKING_FLUTTER.md
@@ -74,7 +74,7 @@ Eventually we'll automate stable, beta and master updates in the cloud.
 Example output from updating 3.7.10 to 3.10.0:
 
 ```
-dart run cutler --no-update --root=$HOME/Documents/GitHub --flutter-channel=beta --dry-run
+dart run cutler rebase --no-update --root=$HOME/Documents/GitHub --flutter-channel=beta --dry-run
 Building package executable... 
 Built cutler:cutler.
 Shorebird stable:
diff --git a/packages/cutler/analysis_options.yaml b/packages/cutler/analysis_options.yaml
index 6fcb3d3b..d9f67a3d 100644
--- a/packages/cutler/analysis_options.yaml
+++ b/packages/cutler/analysis_options.yaml
@@ -1,5 +1 @@
-include: package:very_good_analysis/analysis_options.5.0.0.yaml
-linter:
-  rules:
-    # avoid_print can be removed now that we have a logger.
-    avoid_print: false
+include: package:very_good_analysis/analysis_options.5.0.0.yaml
\ No newline at end of file
diff --git a/packages/cutler/bin/cutler.dart b/packages/cutler/bin/cutler.dart
index 96a8b28a..f3d6afe4 100644
--- a/packages/cutler/bin/cutler.dart
+++ b/packages/cutler/bin/cutler.dart
@@ -1,109 +1,12 @@
-import 'dart:io';
-
-import 'package:args/args.dart';
-import 'package:args/command_runner.dart';
-import 'package:cutler/commands/commands.dart';
-import 'package:cutler/config.dart';
-import 'package:cutler/model.dart';
-import 'package:mason_logger/mason_logger.dart';
-import 'package:path/path.dart' as p;
-
-class Cutler extends CommandRunner<int> {
-  Cutler({Logger? logger})
-      : _logger = logger ?? Logger(),
-        super('cutler', 'A tool for maintaining forks of Flutter.') {
-    addCommand(RebaseCommand(logger: _logger));
-    addCommand(VersionsCommand(logger: _logger));
-
-    argParser
-      ..addFlag('verbose', abbr: 'v')
-      ..addOption(
-        'root',
-        help: 'Directory in which to find checkouts.',
-      )
-      ..addOption(
-        'flutter-channel',
-        defaultsTo: 'stable',
-        help: 'Upstream channel to propose rebasing onto.',
-      )
-      ..addFlag('dry-run', defaultsTo: true, help: 'Do not actually run git.')
-      ..addFlag('update', defaultsTo: true, help: 'Update checkouts.');
-  }
-
-  final Logger _logger;
-
-  Iterable<String> missingDirectories(String rootDir) {
-    return Repo.values.map((repo) => '$rootDir/${repo.path}').where(
-          (path) => !Directory(path).existsSync(),
-        );
-  }
-
-  // This behavior belongs in the Dart SDK somewhere.
-  String findPackageRoot() {
-    // e.g. `dart run bin/cutler.dart`
-    final scriptPath = Platform.script.path;
-    if (scriptPath.endsWith('.dart')) {
-      final cutlerBin = p.dirname(Platform.script.path);
-      return p.dirname(cutlerBin);
-    }
-    // `dart run` pre-compiles into a snapshot and then runs, e.g.
-    // .../packages/cutler/.dart_tool/pub/bin/cutler/cutler.dart-3.0.2.snapshot
-    if (scriptPath.endsWith('.snapshot') && scriptPath.contains('.dart_tool')) {
-      return scriptPath.split('.dart_tool').first;
-    }
-    throw UnimplementedError('Could not find package root.');
-  }
-
-  String fallbackRootDir() {
-    final cutlerRoot = findPackageRoot();
-    final packagesDir = p.dirname(cutlerRoot);
-    final shorebirdDir = p.dirname(packagesDir);
-    final fallbackDirectories = <String>[
-      Directory.current.path,
-      p.dirname(shorebirdDir),
-      // Internal checkouts use a _shorebird wrapper directory.
-      p.dirname(p.dirname(shorebirdDir)),
-    ];
-    for (final directory in fallbackDirectories) {
-      if (missingDirectories(directory).isEmpty) {
-        print('Using $directory as checkouts root.');
-        return directory;
-      }
-    }
-    _logger.err('Failed to find a valid checkouts root, tried:\n'
-        '${fallbackDirectories.join('\n')}');
-    return ''; // Returning an invalid directory will cause validation to fail.
-  }
-
-  @override
-  ArgResults parse(Iterable<String> args) {
-    final results = super.parse(args);
-
-    final rootDir = results['root'] as String? ?? fallbackRootDir();
-
-    final missingDirs = missingDirectories(rootDir);
-    if (missingDirs.isNotEmpty) {
-      _logger
-        ..err('Could not find a valid checkouts root.')
-        ..err('--root must be a directory containing the '
-            'following:\n${Repo.values.map((r) => r.path).join('\n')}')
-        ..err('Missing directories:\n${missingDirs.join('\n')}');
-      exit(1);
-    }
-
-    config = Config(
-      checkoutsRoot: expandUser(rootDir),
-      verbose: results['verbose'] as bool,
-      dryRun: results['dry-run'] as bool,
-      doUpdate: results['update'] as bool,
-      flutterChannel: results['flutter-channel'] as String,
-    );
-
-    return results;
-  }
-}
+import 'package:cutler/cutler.dart';
+import 'package:cutler/logger.dart';
+import 'package:scoped/scoped.dart';
 
 void main(List<String> args) {
-  print(Platform.script.path);
-  Cutler().run(args);
+  runScoped(
+    () => Cutler().run(args),
+    values: {
+      loggerRef,
+    },
+  );
 }
diff --git a/packages/cutler/lib/checkout.dart b/packages/cutler/lib/checkout.dart
new file mode 100644
index 00000000..45016fd9
--- /dev/null
+++ b/packages/cutler/lib/checkout.dart
@@ -0,0 +1,202 @@
+import 'dart:io';
+
+import 'package:cutler/logger.dart';
+import 'package:cutler/model.dart';
+import 'package:path/path.dart' as p;
+
+/// This file provides the git extensions to our model objects for Cutler.
+/// That lets the models be pure data objects, and keeps the command-running
+/// code separate.  Unsure if this is a good design or not.
+
+String runCommand(
+  String executable,
+  List<String> arguments, {
+  String? workingDirectory,
+}) {
+  if (workingDirectory != null && !Directory(workingDirectory).existsSync()) {
+    throw Exception('Directory $workingDirectory does not exist.');
+  }
+
+  final workingDirectoryString = workingDirectory == null ||
+          p.equals(workingDirectory, Directory.current.path)
+      ? ''
+      : ' (in $workingDirectory)';
+  logger.detail("$executable ${arguments.join(' ')}$workingDirectoryString");
+
+  final result = Process.runSync(
+    executable,
+    arguments,
+    workingDirectory: workingDirectory,
+  );
+  if (result.exitCode != 0) {
+    throw Exception(
+      'Failed to run $executable $arguments: ${result.stdout} ${result.stderr}',
+    );
+  }
+  return result.stdout.toString().trim();
+}
+
+/// Represents all the checkouts cutler knows about.
+class Checkouts {
+  /// Constructs a new [Checkouts] object with a given [root] directory.
+  Checkouts(this.root) {
+    for (final repo in Repo.values) {
+      _checkouts[repo] = Checkout(repo, root);
+    }
+  }
+
+  /// The root directory for all checkouts.
+  final String root;
+
+  /// The checkouts.
+  final _checkouts = <Repo, Checkout>{};
+
+  /// Returns an iterable of all checkouts.
+  Iterable<Checkout> get values => _checkouts.values;
+
+  /// Returns a [Checkout] for a given [repo].
+  Checkout operator [](Repo repo) => _checkouts[repo]!;
+
+  /// Returns a [Checkout] for Flutter.
+  Checkout get flutter => _checkouts[Repo.flutter]!;
+
+  /// Returns a [Checkout] for Engine.
+  Checkout get engine => _checkouts[Repo.engine]!;
+
+  /// Returns a [Checkout] for Dart.
+  Checkout get dart => _checkouts[Repo.dart]!;
+
+  /// Returns a [Checkout] for Buildroot.
+  Checkout get buildroot => _checkouts[Repo.buildroot]!;
+
+  /// Returns a [Checkout] for Shorebird.
+  Checkout get shorebird => _checkouts[Repo.shorebird]!;
+}
+
+/// Extension methods for [Repo] to do actual `git` actions.
+class Checkout {
+  /// Constructs a new [Checkout] for a given [repo].
+  Checkout(this.repo, String checkoutsRoot) : _checkoutsRoot = checkoutsRoot;
+
+  /// The repo this checkout is for.
+  final Repo repo;
+
+  /// The root directory for all checkouts.
+  final String _checkoutsRoot;
+
+  /// The name of this repo.
+  String get name => repo.name;
+
+  /// Updates this repo.
+  void fetchAll() {
+    runCommand(
+      'git',
+      ['fetch', '--all', '--tags'],
+      workingDirectory: workingDirectory,
+    );
+  }
+
+  /// Returns a [Version] for the given [commitish].
+  Version versionFrom(String commitish, {bool lookupTags = true}) {
+    final hash = runCommand(
+      'git',
+      ['rev-parse', commitish],
+      workingDirectory: workingDirectory,
+    );
+    return Version(
+      hash: hash,
+      repo: repo,
+      aliases: lookupTags ? getTagsFor(hash) : [],
+    );
+  }
+
+  /// Returns a count of commits between two commits in this repo.
+  int countCommits({required String from, required String to}) {
+    final output = runCommand(
+      'git',
+      ['rev-list', '--count', '$from..$to'],
+      workingDirectory: workingDirectory,
+    );
+    return int.parse(output);
+  }
+
+  /// Returns the working directory for this repo.
+  String get workingDirectory => '$_checkoutsRoot/${repo.path}';
+
+  /// Returns the latest commit for a given [branch] in this repo.
+  String getLatestCommit(String branch) {
+    return runCommand(
+      'git',
+      ['log', '-1', '--pretty=%H', branch],
+      workingDirectory: workingDirectory,
+    );
+  }
+
+  /// Returns the tags for a given [commit] in this repo.
+  List<String> getTagsFor(String commit) {
+    final output = runCommand(
+      'git',
+      ['tag', '--points-at', commit],
+      workingDirectory: workingDirectory,
+    );
+    if (output.isEmpty) {
+      return [];
+    }
+    return output.split('\n');
+  }
+
+  /// Returns the fork point as a [Version] for this repo given a [forkBranch].
+  Version getForkPoint(String forkBranch) {
+    final describeString = runCommand(
+      'git',
+      ['describe', '--tags', forkBranch],
+      workingDirectory: workingDirectory,
+    );
+    final tag = describeString.split('-').first;
+    return versionFrom(tag);
+  }
+
+  /// Returns the contents of a file at a given [path] in this repo at a given
+  /// [commit].
+  String contentsAtPath(String commit, String path) {
+    return runCommand(
+      'git',
+      ['show', '$commit:$path'],
+      workingDirectory: workingDirectory,
+    );
+  }
+
+  /// Writes [contents] to a file at a given [path] in this repo.
+  void writeFile(String path, String contents) {
+    File(p.join(workingDirectory, path)).writeAsStringSync(contents);
+  }
+
+  /// Commits to this repo with a given [message].
+  void commit(String message) {
+    runCommand(
+      'git',
+      ['commit', '-a', '-m', message],
+      workingDirectory: workingDirectory,
+    );
+  }
+
+  /// Returns a [Version] object representing the current HEAD of this repo.
+  Version localHead() {
+    return versionFrom(
+      runCommand(
+        'git',
+        ['rev-parse', 'HEAD'],
+        workingDirectory: workingDirectory,
+      ),
+    );
+  }
+}
+
+/// Extension methods for [Version] to do actual `git` actions.
+// extension VersionCommands on Version {
+//   /// Returns the contents of a file at a given [path] in this repo at this
+//   /// version.
+//   String contentsAtPath(String path) {
+//     return Checkout(repo).contentsAtPath(hash, path);
+//   }
+// }
diff --git a/packages/cutler/lib/commands/base.dart b/packages/cutler/lib/commands/base.dart
index 8ede23e3..c89b6c6d 100644
--- a/packages/cutler/lib/commands/base.dart
+++ b/packages/cutler/lib/commands/base.dart
@@ -1,13 +1,45 @@
 import 'package:args/command_runner.dart';
-import 'package:mason_logger/mason_logger.dart';
+import 'package:cutler/checkout.dart';
+import 'package:cutler/config.dart';
+import 'package:cutler/cutler.dart';
+import 'package:cutler/logger.dart';
 
 /// Base class for Cutler subcommands.
 abstract class CutlerCommand extends Command<int> {
   /// Constructs a new [CutlerCommand].
-  CutlerCommand({
-    required this.logger,
-  });
+  CutlerCommand();
 
-  /// The logger to use for this command.
-  final Logger logger;
+  /// The global config, set during argument parsing.
+  Config get config => (runner! as Cutler).config;
+
+  /// The checkout objects
+  late final Checkouts checkouts;
+
+  /// The Flutter checkout.
+  Checkout get flutter => checkouts.flutter;
+
+  /// The Engine checkout.
+  Checkout get engine => checkouts.engine;
+
+  /// The Shorebird checkout.
+  Checkout get shorebird => checkouts.shorebird;
+
+  /// The Buildroot checkout.
+  Checkout get buildroot => checkouts.buildroot;
+
+  /// The Dart checkout.
+  Checkout get dart => checkouts.dart;
+
+  /// Update the repos if needed.
+  void updateReposIfNeeded(Config config) {
+    if (!config.doUpdate) {
+      return;
+    }
+    final progress = logger.progress('Updating checkouts...');
+    for (final checkout in checkouts.values) {
+      progress.update('Updating ${checkout.name}');
+      checkout.fetchAll();
+    }
+    progress.complete('Checkouts updated!');
+  }
 }
diff --git a/packages/cutler/lib/commands/commands.dart b/packages/cutler/lib/commands/commands.dart
index d381ed63..347422bb 100644
--- a/packages/cutler/lib/commands/commands.dart
+++ b/packages/cutler/lib/commands/commands.dart
@@ -1,2 +1 @@
-export 'rebase_command.dart';
 export 'versions_command.dart';
diff --git a/packages/cutler/lib/commands/rebase_command.dart b/packages/cutler/lib/commands/rebase_command.dart
deleted file mode 100644
index 6dcfcef0..00000000
--- a/packages/cutler/lib/commands/rebase_command.dart
+++ /dev/null
@@ -1,206 +0,0 @@
-import 'package:cutler/commands/base.dart';
-import 'package:cutler/config.dart';
-import 'package:cutler/git_extensions.dart';
-import 'package:cutler/model.dart';
-import 'package:cutler/versions.dart';
-import 'package:io/io.dart';
-
-/// Prints the latest commit for a given [branch] in a given [repo].
-String printLatestForBranch(Repo repo, String branch) {
-  final hash = repo.getLatestCommit(branch);
-  final tags = repo.getTagsFor(hash);
-  final tagsString = tags.isEmpty ? '' : " (${tags.join(', ')})";
-  print('${repo.name.padRight(10)} ${branch.padRight(25)} $hash$tagsString');
-  return hash;
-}
-
-/// Generate rebase commands for the repo given the version sets.
-String rebaseRepo(
-  Repo repo, {
-  required VersionSet forkpoints,
-  required VersionSet upstream,
-  required VersionSet shorebird,
-  bool dryRun = true,
-}) {
-  final run = dryRun ? dryRunCommand : runCommand;
-  if (upstream[repo] != forkpoints[repo]) {
-    print('Rebasing ${repo.name}...');
-    run(
-      'git',
-      [
-        'rebase',
-        '--onto',
-        upstream[repo].ref,
-        forkpoints[repo].ref,
-        shorebird[repo].ref,
-      ],
-      workingDirectory: repo.workingDirectory,
-    );
-
-    return dryRun ? 'new-${repo.name}-hash' : repo.getLatestCommit('HEAD');
-  } else {
-    print('Skipping ${repo.name} (unchanged: ${upstream[repo].ref})');
-  }
-  return shorebird[repo].ref;
-}
-
-/// Print the commands needed to rebase our repos onto the given Flutter
-/// revision.
-class RebaseCommand extends CutlerCommand {
-  /// Constructs a new [RebaseCommand] with a given [logger].
-  RebaseCommand({required super.logger});
-  @override
-  final name = 'rebase';
-  @override
-  final description = 'Rebase our repos onto the latest Flutter.';
-
-  @override
-  int run() {
-    if (config.doUpdate) {
-      print('Updating checkouts (use --no-update to skip)');
-      for (final repo in Repo.values) {
-        print('Updating ${repo.name}...');
-        repo.fetchAll();
-      }
-    }
-
-    final shorebirdStable =
-        Repo.shorebird.getLatestCommit(config.shorebirdReleaseBranch);
-    final shorebirdFlutter = Repo.shorebird
-        .contentsAtPath(shorebirdStable, 'bin/internal/flutter.version');
-    final shorebird = getFlutterVersions(shorebirdFlutter);
-    print('Shorebird stable:');
-    printVersions(shorebird, indent: 2);
-
-    final flutterForkpoint = Repo.flutter.getForkPoint(shorebird.flutter.hash);
-    // This is slightly error-prone in that we're assuming that our engine and
-    // buildroot forks started from the correct commit.  But I'm not sure how
-    // to determine the forkpoint otherwise.  engine and buildroot don't have
-    // a stable branch, yet they do seem to "branch" for stable releases at the
-    // x.x.0 release.
-    final forkpoints = getFlutterVersions(flutterForkpoint.hash);
-    print('Forkpoints:');
-    printVersions(forkpoints, indent: 2);
-
-    // Figure out the latest version of Flutter.
-    final upstreamFlutter =
-        Repo.flutter.getLatestCommit('upstream/${config.flutterChannel}');
-    // Figure out what versions that Flutter depends on.
-    final upstream = getFlutterVersions(upstreamFlutter);
-    print('Upstream ${config.flutterChannel}:');
-    printVersions(upstream, indent: 2);
-
-    Version doRebase(Repo repo) {
-      final newHash = rebaseRepo(
-        repo,
-        forkpoints: forkpoints,
-        upstream: upstream,
-        shorebird: shorebird,
-        dryRun: config.dryRun,
-      );
-      return repo.versionFrom(newHash, lookupTags: !config.dryRun);
-    }
-
-    // Rebase our repos.
-    // These are done in a very specific order.
-    var newHead = VersionSet(
-      buildroot: doRebase(Repo.buildroot),
-      dart: doRebase(Repo.dart),
-      engine: doRebase(Repo.engine),
-      flutter: doRebase(Repo.flutter),
-    );
-    // Make sure engine points to this buildroot.
-    // If not, update it and commit.
-    if (shorebird[Repo.buildroot] != newHead.buildroot) {
-      print('Updating engine DEPS...');
-      final depsContents =
-          shorebird[Repo.engine].contentsAtPath(Paths.engineDEPS.path);
-      final newDepsContents = depsContents.replaceAll(
-        shorebird[Repo.buildroot].hash,
-        newHead.buildroot.hash,
-      );
-      if (newDepsContents != depsContents) {
-        if (config.dryRun) {
-          print('Would have changed DEPS lines:');
-          final changes = newDepsContents.split('\n').where((line) {
-            return line.contains(newHead.buildroot.hash);
-          });
-          print(changes);
-        } else {
-          Repo.engine.writeFile(Paths.engineDEPS.path, newDepsContents);
-          Repo.engine.commit('Update DEPS.');
-        }
-      } else {
-        print('ERROR: engine DEPS is already up to date?');
-        return ExitCode.software.code;
-      }
-      newHead = newHead.copyWith(engine: Repo.engine.localHead());
-    }
-
-    // Update our forked flutter's engine version.
-    if (shorebird[Repo.engine] != newHead.engine) {
-      print('Updating flutter engine version...');
-      final existingEngineVersion = shorebird[Repo.flutter]
-          .contentsAtPath(Paths.flutterEngineVersion.path)
-          .trim();
-      if (newHead.engine.hash != existingEngineVersion) {
-        if (config.dryRun) {
-          print(
-            '  Change engine.version: ${newHead.engine.hash} from '
-            '$existingEngineVersion',
-          );
-        } else {
-          Repo.flutter
-              .writeFile(Paths.flutterEngineVersion.path, newHead.engine.hash);
-          Repo.flutter.commit('Update engine.version');
-        }
-      } else {
-        print('ERROR: flutter engine.version is already up to date?');
-        return ExitCode.software.code;
-      }
-      newHead = newHead.copyWith(flutter: Repo.flutter.localHead());
-    }
-    // Update Shorebird's version of Flutter.
-    if (shorebird[Repo.flutter] != newHead.flutter) {
-      print('Updating shorebird flutter version...');
-      if (config.dryRun) {
-        print(
-          '  Change flutter.version: ${newHead.flutter.hash} from '
-          '${shorebird[Repo.flutter].hash}',
-        );
-      } else {
-        Repo.shorebird.writeFile(
-          Paths.shorebirdFlutterVersion.path,
-          newHead.flutter.hash,
-        );
-        Repo.shorebird.commit('Update flutter.version');
-      }
-    }
-
-    // To push a new engine:
-    // git branch stable_codepush HEAD --force
-    // git push origin stable_codepush --force
-
-    // Engine rev: d470ae25d21f583abe128f7b838476afd5e45bde
-
-    // To push new flutter:
-    // % git rebase --onto 3.7.12 3.7.10 \
-    // 45fc514f1a9c347a3af76b02baf980a4d88b7879
-    // Auto-merging bin/internal/engine.version
-    // CONFLICT (content): Merge conflict in bin/internal/engine.version
-    // error: could not apply c2185f5f6c... chore: Update engine version to
-    // shorebird-3.7.10
-    // hint: Resolve all conflicts manually, mark them as resolved with
-    // hint: "git add/rm <conflicted_files>", then run "git rebase --continue".
-    // hint: You can instead skip this commit: run "git rebase --skip".
-    // hint: To abort and get back to the state before "git rebase", run "git
-    // rebase --abort".
-    // Could not apply c2185f5f6c... chore: Update engine version to
-    // shorebird-3.7.10
-
-    // Flutter revision: 58dff390738f9c512ab7e0638af9573515b0409c
-
-    // To push new shorebird:
-    return ExitCode.success.code;
-  }
-}
diff --git a/packages/cutler/lib/commands/versions_command.dart b/packages/cutler/lib/commands/versions_command.dart
index 62166ef2..de730c16 100644
--- a/packages/cutler/lib/commands/versions_command.dart
+++ b/packages/cutler/lib/commands/versions_command.dart
@@ -1,6 +1,6 @@
+import 'package:cutler/checkout.dart';
 import 'package:cutler/commands/base.dart';
-import 'package:cutler/config.dart';
-import 'package:cutler/git_extensions.dart';
+import 'package:cutler/logger.dart';
 import 'package:cutler/model.dart';
 import 'package:cutler/versions.dart';
 import 'package:io/io.dart';
@@ -8,7 +8,7 @@ import 'package:io/io.dart';
 /// Print the versions a given Shorebird or Flutter hash depends on.
 class VersionsCommand extends CutlerCommand {
   /// Constructs a new [VersionsCommand] with a given [logger].
-  VersionsCommand({required super.logger}) {
+  VersionsCommand() {
     argParser.addOption(
       'repo',
       abbr: 'r',
@@ -25,47 +25,44 @@ class VersionsCommand extends CutlerCommand {
 
   @override
   int run() {
+    checkouts = Checkouts(config.checkoutsRoot);
+
     final repoName = argResults!['repo'] as String;
     final repo = Repo.values.firstWhere((r) => r.name == repoName);
     final isShorebird = repo.name == 'shorebird';
     late final String hash;
     if (argResults!.rest.isEmpty) {
-      if (isShorebird) {
-        print('No version hash provided, using Shorebird `origin/stable`.');
-        hash = 'origin/stable';
-      } else {
-        print('No version hash provided, using Flutter `upstream/stable`.');
-        hash = 'upstream/stable';
-      }
+      hash = isShorebird ? 'origin/stable' : 'upstream/stable';
     } else {
       hash = argResults!.rest.first;
     }
 
-    if (config.doUpdate) {
-      print('Updating checkouts (use --no-update to skip)');
-      for (final repo in Repo.values) {
-        print('Updating ${repo.name}...');
-        repo.fetchAll();
-      }
+    updateReposIfNeeded(config);
+
+    if (!isShorebird) {
+      final flutterVersions = getFlutterVersions(checkouts, hash);
+      logger.info('Flutter $hash:');
+      printVersions(checkouts, flutterVersions, indent: 2);
+      return ExitCode.success.code;
     }
 
-    late final String flutterHash;
-    if (isShorebird) {
-      final shorebirdFlutter =
-          Repo.shorebird.contentsAtPath(hash, 'bin/internal/flutter.version');
-      final shorebird = getFlutterVersions(shorebirdFlutter);
-      logger.info('Shorebird $hash:');
-      printVersions(shorebird, indent: 2);
-      final flutterForkpoint =
-          Repo.flutter.getForkPoint(shorebird.flutter.hash);
-      flutterHash = flutterForkpoint.hash;
-    } else {
-      flutterHash = hash;
-    }
+    final shorebirdFlutter =
+        shorebird.contentsAtPath(hash, 'bin/internal/flutter.version');
+    final shorebirdVersions = getFlutterVersions(checkouts, shorebirdFlutter);
+    final flutterForkpoint =
+        flutter.getForkPoint(shorebirdVersions.flutter.hash);
+    final flutterHash = flutterForkpoint.hash;
+    final flutterVersions = getFlutterVersions(checkouts, flutterHash);
 
-    final flutterVersions = getFlutterVersions(flutterHash);
-    logger.info('Flutter $flutterHash:');
-    printVersions(flutterVersions, indent: 2);
+    logger.info('Shorebird @ $hash');
+    printVersions(
+      checkouts,
+      shorebirdVersions,
+      indent: 2,
+      upstream: flutterVersions,
+    );
+    logger.info('\nUpstream');
+    printVersions(checkouts, flutterVersions, indent: 2);
 
     return ExitCode.success.code;
   }
diff --git a/packages/cutler/lib/config.dart b/packages/cutler/lib/config.dart
index 5f96f346..12f53797 100644
--- a/packages/cutler/lib/config.dart
+++ b/packages/cutler/lib/config.dart
@@ -1,5 +1,7 @@
 import 'dart:io';
 
+import 'package:path/path.dart' as p;
+
 // https://github.com/dart-lang/sdk/issues/18466
 // https://github.com/dart-lang/path/issues/117#issuecomment-1034313012
 /// Expands a path that may contain a user directory (`~`). If [env] is
@@ -21,13 +23,34 @@ String expandUser(String path, {Map<String, String>? env}) {
   return path;
 }
 
+// This behavior belongs in the Dart SDK somewhere.
+/// Find the package root for the current running script.
+String findPackageRoot() {
+  // e.g. `dart run bin/cutler.dart`
+  final scriptPath = Platform.script.path;
+  if (scriptPath.endsWith('.dart')) {
+    final cutlerBin = p.dirname(Platform.script.path);
+    return p.dirname(cutlerBin);
+  }
+  // `dart run` pre-compiles into a snapshot and then runs, e.g.
+  // .../packages/cutler/.dart_tool/pub/bin/cutler/cutler.dart-3.0.2.snapshot
+  if (scriptPath.endsWith('.snapshot') && scriptPath.contains('.dart_tool')) {
+    return scriptPath.split('.dart_tool').first;
+  }
+  // package test has scriptPath ending in .dill, e.g.
+  // /var/folders/fv/fqqmfjqd6zvdqrbrv78gt4m80000gn/T/dart_test.kernel.PhFW66/test.dart_4.dill
+  if (scriptPath.endsWith('.dill')) {
+    throw UnimplementedError('Running inside a test');
+  }
+  throw UnimplementedError('Could not find package root: $scriptPath');
+}
+
 // Config is basically just our typed ArgResults held as a global.
 /// Global configuration object for Cutler.
 class Config {
   /// Constructs a new [Config].
   Config({
     required this.checkoutsRoot,
-    required this.verbose,
     required this.dryRun,
     required this.doUpdate,
     required this.flutterChannel,
@@ -36,9 +59,6 @@ class Config {
   /// The root directory where checkouts can be found.
   final String checkoutsRoot;
 
-  /// Whether to print verbose output.
-  final bool verbose;
-
   /// Whether to perform a dry run.
   final bool dryRun;
 
@@ -51,6 +71,3 @@ class Config {
   /// The name of the release branch for Shorebird.
   final String shorebirdReleaseBranch = 'origin/stable';
 }
-
-/// The global configuration object for Cutler.
-late final Config config;
diff --git a/packages/cutler/lib/cutler.dart b/packages/cutler/lib/cutler.dart
new file mode 100644
index 00000000..f270d776
--- /dev/null
+++ b/packages/cutler/lib/cutler.dart
@@ -0,0 +1,94 @@
+import 'dart:io';
+
+import 'package:args/args.dart';
+import 'package:args/command_runner.dart';
+import 'package:cutler/commands/commands.dart';
+import 'package:cutler/config.dart';
+import 'package:cutler/logger.dart';
+import 'package:cutler/model.dart';
+import 'package:mason_logger/mason_logger.dart';
+import 'package:path/path.dart' as p;
+
+/// The main Cutler command runner.
+class Cutler extends CommandRunner<int> {
+  /// Constructs a new [Cutler] command runner.
+  Cutler() : super('cutler', 'A tool for maintaining forks of Flutter.') {
+    addCommand(VersionsCommand());
+
+    argParser
+      ..addFlag('verbose', abbr: 'v')
+      ..addOption(
+        'root',
+        help: 'Directory in which to find checkouts.',
+      )
+      ..addOption(
+        'flutter-channel',
+        defaultsTo: 'stable',
+        help: 'Upstream channel to propose rebasing onto.',
+      )
+      ..addFlag('dry-run', defaultsTo: true, help: 'Do not actually run git.')
+      ..addFlag('update', defaultsTo: true, help: 'Update checkouts.');
+  }
+
+  /// Global config set during arg parsing.
+  late Config config;
+
+  /// Lists directories missing from the proposed root directory.
+  Iterable<String> missingDirectories(String rootDir) {
+    return Repo.values.map((repo) => '$rootDir/${repo.path}').where(
+          (path) => !Directory(path).existsSync(),
+        );
+  }
+
+  /// Find a valid root directory for checkouts.
+  String fallbackRootDir() {
+    final cutlerRoot = findPackageRoot();
+    final packagesDir = p.dirname(cutlerRoot);
+    final shorebirdDir = p.dirname(packagesDir);
+    final fallbackDirectories = <String>[
+      Directory.current.path,
+      p.dirname(shorebirdDir),
+      // Internal checkouts use a _shorebird wrapper directory.
+      p.dirname(p.dirname(shorebirdDir)),
+    ];
+    for (final directory in fallbackDirectories) {
+      if (missingDirectories(directory).isEmpty) {
+        logger.info('Using $directory as checkouts root.');
+        return directory;
+      }
+    }
+    logger.err('Failed to find a valid checkouts root, tried:\n'
+        '${fallbackDirectories.join('\n')}');
+    return ''; // Returning an invalid directory will cause validation to fail.
+  }
+
+  @override
+  ArgResults parse(Iterable<String> args) {
+    final results = super.parse(args);
+
+    final rootDir = results['root'] as String? ?? fallbackRootDir();
+
+    final missingDirs = missingDirectories(rootDir);
+    if (missingDirs.isNotEmpty) {
+      logger
+        ..err('Could not find a valid checkouts root.')
+        ..err('--root must be a directory containing the '
+            'following:\n${Repo.values.map((r) => r.path).join('\n')}')
+        ..err('Missing directories:\n${missingDirs.join('\n')}');
+      exit(1);
+    }
+
+    config = Config(
+      checkoutsRoot: expandUser(rootDir),
+      dryRun: results['dry-run'] as bool,
+      doUpdate: results['update'] as bool,
+      flutterChannel: results['flutter-channel'] as String,
+    );
+
+    if (results['verbose'] as bool) {
+      logger.level = Level.verbose;
+    }
+
+    return results;
+  }
+}
diff --git a/packages/cutler/lib/git_extensions.dart b/packages/cutler/lib/git_extensions.dart
deleted file mode 100644
index fbe48eee..00000000
--- a/packages/cutler/lib/git_extensions.dart
+++ /dev/null
@@ -1,145 +0,0 @@
-import 'dart:io';
-
-import 'package:cutler/config.dart';
-import 'package:cutler/model.dart';
-import 'package:path/path.dart' as p;
-
-/// This file provides the git extensions to our model objects for Cutler.
-/// That lets the models be pure data objects, and keeps the command-running
-/// code separate.  Unsure if this is a good design or not.
-
-String runCommand(
-  String executable,
-  List<String> arguments, {
-  String? workingDirectory,
-}) {
-  if (workingDirectory != null && !Directory(workingDirectory).existsSync()) {
-    throw Exception('Directory $workingDirectory does not exist.');
-  }
-
-  if (config.verbose) {
-    final workingDirectoryString = workingDirectory == null ||
-            p.equals(workingDirectory, Directory.current.path)
-        ? ''
-        : ' (in $workingDirectory)';
-    print("$executable ${arguments.join(' ')}$workingDirectoryString");
-  }
-  final result = Process.runSync(
-    executable,
-    arguments,
-    workingDirectory: workingDirectory,
-  );
-  if (result.exitCode != 0) {
-    throw Exception('Failed to run $executable $arguments: ${result.stderr}');
-  }
-  return result.stdout.toString().trim();
-}
-
-/// Function to print the command that would be run, but not actually run it.
-void dryRunCommand(
-  String executable,
-  List<String> arguments, {
-  String? workingDirectory,
-}) {
-  print("$executable ${arguments.join(' ')}");
-}
-
-/// Extension methods for [Repo] to do actual `git` actions.
-extension RepoCommands on Repo {
-  /// Updates this repo.
-  void fetchAll() {
-    runCommand(
-      'git',
-      ['fetch', '--all'],
-      workingDirectory: workingDirectory,
-    );
-  }
-
-  /// Returns a [Version] for the given [hash].
-  Version versionFrom(String hash, {bool lookupTags = true}) {
-    return Version(
-      hash: hash,
-      repo: this,
-      aliases: lookupTags ? getTagsFor(hash) : [],
-    );
-  }
-
-  /// Returns the working directory for this repo.
-  String get workingDirectory => '${config.checkoutsRoot}/$path';
-
-  /// Returns the latest commit for a given [branch] in this repo.
-  String getLatestCommit(String branch) {
-    return runCommand(
-      'git',
-      ['log', '-1', '--pretty=%H', branch],
-      workingDirectory: workingDirectory,
-    );
-  }
-
-  /// Returns the tags for a given [commit] in this repo.
-  List<String> getTagsFor(String commit) {
-    final output = runCommand(
-      'git',
-      ['tag', '--points-at', commit],
-      workingDirectory: workingDirectory,
-    );
-    if (output.isEmpty) {
-      return [];
-    }
-    return output.split('\n');
-  }
-
-  /// Returns the fork point as a [Version] for this repo given a [forkBranch].
-  Version getForkPoint(String forkBranch) {
-    final hash = runCommand(
-      'git',
-      ['merge-base', upstreamBranch, forkBranch],
-      workingDirectory: workingDirectory,
-    );
-    return versionFrom(hash);
-  }
-
-  /// Returns the contents of a file at a given [path] in this repo at a given
-  /// [commit].
-  String contentsAtPath(String commit, String path) {
-    return runCommand(
-      'git',
-      ['show', '$commit:$path'],
-      workingDirectory: workingDirectory,
-    );
-  }
-
-  /// Writes [contents] to a file at a given [path] in this repo.
-  void writeFile(String path, String contents) {
-    File(path).writeAsStringSync(contents);
-  }
-
-  /// Commits to this repo with a given [message].
-  void commit(String message) {
-    runCommand(
-      'git',
-      ['commit', '-a', '-m', message],
-      workingDirectory: workingDirectory,
-    );
-  }
-
-  /// Returns a [Version] object representing the current HEAD of this repo.
-  Version localHead() {
-    return versionFrom(
-      runCommand(
-        'git',
-        ['rev-parse', 'HEAD'],
-        workingDirectory: workingDirectory,
-      ),
-    );
-  }
-}
-
-/// Extension methods for [Version] to do actual `git` actions.
-extension VersionCommands on Version {
-  /// Returns the contents of a file at a given [path] in this repo at this
-  /// version.
-  String contentsAtPath(String path) {
-    return repo.contentsAtPath(hash, path);
-  }
-}
diff --git a/packages/cutler/lib/logger.dart b/packages/cutler/lib/logger.dart
new file mode 100644
index 00000000..f09f7e54
--- /dev/null
+++ b/packages/cutler/lib/logger.dart
@@ -0,0 +1,8 @@
+import 'package:mason_logger/mason_logger.dart';
+import 'package:scoped/scoped.dart';
+
+/// A reference to a [Logger] instance.
+final loggerRef = create(Logger.new);
+
+/// The [Logger] instance available in the current zone.
+Logger get logger => read(loggerRef);
diff --git a/packages/cutler/lib/versions.dart b/packages/cutler/lib/versions.dart
index 79ba8968..8499d681 100644
--- a/packages/cutler/lib/versions.dart
+++ b/packages/cutler/lib/versions.dart
@@ -1,8 +1,15 @@
-import 'package:cutler/git_extensions.dart';
+import 'package:collection/collection.dart';
+import 'package:cutler/checkout.dart';
+import 'package:cutler/logger.dart';
 import 'package:cutler/model.dart';
 
 /// Print VersionSet [versions] to stdout at a given [indent] level.
-void printVersions(VersionSet versions, {int indent = 0}) {
+void printVersions(
+  Checkouts checkouts,
+  VersionSet versions, {
+  int indent = 0,
+  VersionSet? upstream,
+}) {
   final repos = [
     Repo.flutter,
     Repo.engine,
@@ -10,7 +17,20 @@ void printVersions(VersionSet versions, {int indent = 0}) {
     Repo.buildroot,
   ];
   for (final repo in repos) {
-    print("${' ' * indent}${repo.name.padRight(9)} ${versions[repo]}");
+    final checkout = checkouts[repo];
+    final string = "${' ' * indent}${repo.name.padRight(9)} ${versions[repo]}";
+    // Include number of commits ahead of upstream.
+    if (upstream != null) {
+      final upstreamVersion = upstream[repo];
+      final commitCount = checkout.countCommits(
+        from: upstreamVersion.ref,
+        to: versions[repo].ref,
+      );
+      final commitsString = commitCount != 0 ? ' ($commitCount ahead)' : '';
+      logger.info('$string$commitsString');
+    } else {
+      logger.info(string);
+    }
   }
 }
 
@@ -18,19 +38,21 @@ void printVersions(VersionSet versions, {int indent = 0}) {
 /// e.g. `flutterHash` might be `origin/stable` or `v1.22.0-12.1.pre`.
 /// and this would return the set of versions (engine and buildroot) that
 /// Flutter depends on for that release.
-VersionSet getFlutterVersions(String flutterHash) {
-  final engineHash = Repo.flutter
-      .contentsAtPath(flutterHash, 'bin/internal/engine.version')
-      .trim();
-  final depsContents =
-      Repo.engine.contentsAtPath(engineHash, Paths.engineDEPS.path);
+VersionSet getFlutterVersions(Checkouts checkouts, String flutterHash) {
+  final flutter = checkouts.flutter;
+  final engine = checkouts.engine;
+  final buildroot = checkouts.buildroot;
+  final dart = checkouts.dart;
+  final engineHash =
+      flutter.contentsAtPath(flutterHash, 'bin/internal/engine.version').trim();
+  final depsContents = engine.contentsAtPath(engineHash, Paths.engineDEPS.path);
   final buildrootHash = parseBuildrootRevision(depsContents);
   final dartHash = parseDartRevision(depsContents);
   return VersionSet(
-    engine: Repo.engine.versionFrom(engineHash),
-    flutter: Repo.flutter.versionFrom(flutterHash),
-    buildroot: Repo.buildroot.versionFrom(buildrootHash),
-    dart: Repo.dart.versionFrom(dartHash),
+    engine: engine.versionFrom(engineHash),
+    flutter: flutter.versionFrom(flutterHash),
+    buildroot: buildroot.versionFrom(buildrootHash),
+    dart: dart.versionFrom(dartHash),
   );
 }
 
@@ -52,8 +74,13 @@ String parseBuildrootRevision(String depsContents) {
 String parseDartRevision(String depsContents) {
   final lines = depsContents.split('\n');
   // Example:
-  //  'dart_revision': 'ce926bc6dcf649bd31a396e4e3961196115727cd',
-  final dartLine =
+  //  'dart_sdk_revision': 'ce926bc6dcf649bd31a396e4e3961196115727cd',
+  // In our fork we use dart_sdk_revision, not dart_revision, since the former
+  // points to our fork of the Dart SDK and the latter points to some base
+  // revision for dart.googlesource.com/sdk.
+  // For upstream we use 'dart_revision'.
+  final dartLine = lines
+          .firstWhereOrNull((line) => line.contains("'dart_sdk_revision': ")) ??
       lines.firstWhere((line) => line.contains("'dart_revision': "));
   final regexp = RegExp('([0-9a-f]{40})');
   final match = regexp.firstMatch(dartLine);
diff --git a/packages/cutler/pubspec.lock b/packages/cutler/pubspec.lock
index 70f4c2db..3f7e463d 100644
--- a/packages/cutler/pubspec.lock
+++ b/packages/cutler/pubspec.lock
@@ -42,7 +42,7 @@ packages:
     source: hosted
     version: "2.1.1"
   collection:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: collection
       sha256: ee67cb0715911d28db6bf4af1026078bd6f0128b07a5f66fb2ed94ec6783c09a
@@ -169,6 +169,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.0.4"
+  mocktail:
+    dependency: "direct main"
+    description:
+      name: mocktail
+      sha256: "9503969a7c2c78c7292022c70c0289ed6241df7a9ba720010c0b215af29a5a58"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.0.0"
   node_preamble:
     dependency: transitive
     description:
@@ -209,6 +217,13 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.1.4"
+  scoped:
+    dependency: "direct main"
+    description:
+      path: "../scoped"
+      relative: true
+    source: path
+    version: "0.1.0+1"
   shelf:
     dependency: transitive
     description:
@@ -341,10 +356,10 @@ packages:
     dependency: transitive
     description:
       name: vm_service
-      sha256: "0fae432c85c4ea880b33b497d32824b97795b04cdaa74d270219572a1f50268d"
+      sha256: c538be99af830f478718b51630ec1b6bee5e74e52c8a802d328d9e71d35d2583
       url: "https://pub.dev"
     source: hosted
-    version: "11.9.0"
+    version: "11.10.0"
   watcher:
     dependency: transitive
     description:
diff --git a/packages/cutler/pubspec.yaml b/packages/cutler/pubspec.yaml
index 90da13b5..2919c1ce 100644
--- a/packages/cutler/pubspec.yaml
+++ b/packages/cutler/pubspec.yaml
@@ -2,6 +2,7 @@ name: cutler
 description: A tool for managing Flutter forks.
 version: 1.0.0
 repository: https://github.com/shorebirdtech/shorebird
+publish_to: none
 
 environment:
   sdk: '>=3.0.0 <4.0.0'
@@ -12,7 +13,11 @@ dev_dependencies:
 
 dependencies:
   args: ^2.4.0
+  collection: ^1.18.0
   io: ^1.0.4
   mason_logger: ^0.2.6
   meta: ^1.9.1
+  mocktail: ^1.0.0
   path: ^1.8.3
+  scoped:
+    path: ../scoped
diff --git a/packages/cutler/test/checkout_test.dart b/packages/cutler/test/checkout_test.dart
new file mode 100644
index 00000000..c8853dd2
--- /dev/null
+++ b/packages/cutler/test/checkout_test.dart
@@ -0,0 +1,97 @@
+import 'dart:io';
+
+import 'package:cutler/checkout.dart';
+import 'package:cutler/logger.dart';
+import 'package:cutler/model.dart';
+import 'package:mason_logger/mason_logger.dart';
+import 'package:mocktail/mocktail.dart';
+import 'package:scoped/scoped.dart';
+import 'package:test/test.dart';
+
+class _MockLogger extends Mock implements Logger {}
+
+void main() {
+  test('runCommand', () {
+    final dartPath = Platform.executable;
+    expect(
+      () => runCommand(dartPath, [], workingDirectory: 'DOES_NOT_EXIST'),
+      throwsA(isA<Exception>()),
+    );
+  });
+
+  test('runCommand with git', () {
+    final systemTemp = Directory.systemTemp;
+    final temp = systemTemp.createTempSync();
+    // Should this use something like:
+    // https://pub.dev/packages/process_run?
+    // or https://dcli.onepub.dev/dcli-api/calling-apps#which
+    const gitPath = 'git';
+    final result = runScoped(
+      () {
+        return runCommand(gitPath, ['init'], workingDirectory: temp.path);
+      },
+      values: {
+        loggerRef.overrideWith(_MockLogger.new),
+      },
+    );
+    expect(result, contains('Initialized empty Git repository'));
+  });
+
+  test('Checkouts', () {
+    final checkouts = Checkouts('ROOT');
+    expect(checkouts.dart.name, 'dart');
+    expect(checkouts.engine.name, 'engine');
+    expect(checkouts.flutter.name, 'flutter');
+    expect(checkouts.buildroot.name, 'buildroot');
+    expect(checkouts.shorebird.name, 'shorebird');
+    expect(checkouts.values.length, 5);
+    expect(checkouts.buildroot.workingDirectory, 'ROOT/engine/src');
+    expect(checkouts.engine.workingDirectory, 'ROOT/engine/src/flutter');
+    expect(checkouts.dart.workingDirectory, 'ROOT/engine/src/third_party/dart');
+    expect(checkouts.flutter.workingDirectory, 'ROOT/flutter');
+    expect(checkouts.shorebird.workingDirectory, 'ROOT/_shorebird/shorebird');
+  });
+
+  Directory setupCheckouts() {
+    final systemTemp = Directory.systemTemp;
+    final checkoutsRoot = systemTemp.createTempSync();
+    for (final repo in Repo.values) {
+      final dir = Directory('${checkoutsRoot.path}/${repo.path}')
+        ..createSync(recursive: true);
+      runCommand('git', ['init'], workingDirectory: dir.path);
+      final checkout = Checkout(repo, checkoutsRoot.path)
+        ..writeFile('NAME', repo.name);
+      runCommand('git', ['add', 'NAME'], workingDirectory: dir.path);
+      // Git requires user.email user.name to be set before committing.
+      runCommand(
+        'git',
+        ['config', 'user.email', 'test@shorebird.dev'],
+        workingDirectory: dir.path,
+      );
+      runCommand(
+        'git',
+        ['config', 'user.name', 'Cutler Checkout Test'],
+        workingDirectory: dir.path,
+      );
+      checkout.commit('Test commit');
+    }
+    return checkoutsRoot;
+  }
+
+  test('Checkouts real git commands', () {
+    runScoped(
+      () {
+        final root = setupCheckouts();
+        final checkouts = Checkouts(root.path);
+        expect(checkouts.dart.contentsAtPath('HEAD', 'NAME'), 'dart');
+        expect(checkouts.engine.contentsAtPath('HEAD', 'NAME'), 'engine');
+        expect(checkouts.flutter.contentsAtPath('HEAD', 'NAME'), 'flutter');
+        expect(checkouts.buildroot.contentsAtPath('HEAD', 'NAME'), 'buildroot');
+        expect(checkouts.shorebird.contentsAtPath('HEAD', 'NAME'), 'shorebird');
+      },
+      values: {
+        loggerRef.overrideWith(_MockLogger.new),
+      },
+    );
+  });
+}
diff --git a/packages/cutler/test/cutler_test.dart b/packages/cutler/test/cutler_test.dart
index 9b232a44..1f2e59a1 100644
--- a/packages/cutler/test/cutler_test.dart
+++ b/packages/cutler/test/cutler_test.dart
@@ -5,5 +5,22 @@ void main() {
   test('expandUser', () {
     final path = expandUser('~/foo/bar', env: {'HOME': '/home/user'});
     expect(path, endsWith('/home/user/foo/bar'));
+
+    // HOME is not set.
+    expect(() => expandUser('~/foo/bar', env: {}), throwsA(isA<Exception>()));
+  });
+
+  test('findPackageRoot', () {
+    // Should throw an exception with the string 'test' in it.
+    expect(
+      findPackageRoot,
+      throwsA(
+        isA<UnimplementedError>().having(
+          (e) => e.message,
+          'message',
+          contains('test'),
+        ),
+      ),
+    );
   });
 }
diff --git a/packages/cutler/test/model_test.dart b/packages/cutler/test/model_test.dart
new file mode 100644
index 00000000..793812e7
--- /dev/null
+++ b/packages/cutler/test/model_test.dart
@@ -0,0 +1,99 @@
+import 'package:cutler/model.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('Version', () {
+    const one = Version(
+      repo: Repo.flutter,
+      hash: 'abc123',
+    );
+    const two = Version(
+      repo: Repo.flutter,
+      hash: 'abc123',
+      aliases: ['foo', 'bar'],
+    );
+    const three = Version(
+      repo: Repo.flutter,
+      hash: 'def456',
+    );
+    expect(one, equals(two));
+    expect(one, isNot(equals(three)));
+    expect(one.hashCode, equals(two.hashCode));
+    expect(one.hashCode, isNot(equals(three.hashCode)));
+
+    expect(one.ref, equals('abc123'));
+    expect(two.ref, equals('foo'));
+    expect(three.ref, equals('def456'));
+
+    expect(one.toString(), equals('abc123'));
+    expect(two.toString(), equals('abc123 (foo, bar)'));
+    expect(three.toString(), equals('def456'));
+  });
+
+  test('VersionSet', () {
+    const one = VersionSet(
+      engine: Version(
+        repo: Repo.engine,
+        hash: 'e1',
+      ),
+      flutter: Version(
+        repo: Repo.flutter,
+        hash: 'f1',
+      ),
+      buildroot: Version(
+        repo: Repo.buildroot,
+        hash: 'b1',
+      ),
+      dart: Version(
+        repo: Repo.dart,
+        hash: 'd1',
+      ),
+    );
+    final two = one.copyWith(
+      engine: const Version(
+        repo: Repo.engine,
+        hash: 'e2',
+      ),
+      flutter: const Version(
+        repo: Repo.flutter,
+        hash: 'f2',
+      ),
+      buildroot: const Version(
+        repo: Repo.buildroot,
+        hash: 'b2',
+      ),
+      dart: const Version(
+        repo: Repo.dart,
+        hash: 'd2',
+      ),
+    );
+    expect(one, isNot(equals(two)));
+    expect(one.hashCode, isNot(equals(two.hashCode)));
+    expect(
+      one[Repo.engine],
+      equals(const Version(repo: Repo.engine, hash: 'e1')),
+    );
+    expect(
+      one[Repo.flutter],
+      equals(const Version(repo: Repo.flutter, hash: 'f1')),
+    );
+    expect(
+      one[Repo.buildroot],
+      equals(const Version(repo: Repo.buildroot, hash: 'b1')),
+    );
+    expect(one[Repo.dart], equals(const Version(repo: Repo.dart, hash: 'd1')));
+    expect(
+      two[Repo.engine],
+      equals(const Version(repo: Repo.engine, hash: 'e2')),
+    );
+    expect(
+      two[Repo.flutter],
+      equals(const Version(repo: Repo.flutter, hash: 'f2')),
+    );
+    expect(
+      two[Repo.buildroot],
+      equals(const Version(repo: Repo.buildroot, hash: 'b2')),
+    );
+    expect(two[Repo.dart], equals(const Version(repo: Repo.dart, hash: 'd2')));
+  });
+}