feat(checkout): add bindings and api

test/checkout_test.dart

@@ -0,0 +1,96 @@
+import 'dart:io';
+import 'package:libgit2dart/src/git_types.dart';
+import 'package:test/test.dart';
+import 'package:libgit2dart/libgit2dart.dart';
+import 'helpers/util.dart';
+
+void main() {
+  late Repository repo;
+  final tmpDir = '${Directory.systemTemp.path}/checkout_testrepo/';
+
+  setUp(() async {
+    if (await Directory(tmpDir).exists()) {
+      await Directory(tmpDir).delete(recursive: true);
+    }
+    await copyRepo(
+      from: Directory('test/assets/testrepo/'),
+      to: await Directory(tmpDir).create(),
+    );
+    repo = Repository.open(tmpDir);
+  });
+
+  tearDown(() async {
+    repo.free();
+    await Directory(tmpDir).delete(recursive: true);
+  });
+
+  group('Checkout', () {
+    test('successfully checkouts head', () {
+      File('${tmpDir}feature_file').writeAsStringSync('edit');
+      expect(repo.status, contains('feature_file'));
+
+      repo.checkout(refName: 'HEAD', strategy: [GitCheckout.force]);
+      expect(repo.status, isEmpty);
+    });
+
+    test('successfully checkouts index', () {
+      File('${repo.workdir}feature_file').writeAsStringSync('edit');
+      expect(repo.status, contains('feature_file'));
+
+      repo.checkout(strategy: [GitCheckout.force]);
+      expect(repo.status, isEmpty);
+    });
+
+    test('successfully checkouts tree', () {
+      final masterHead =
+          repo['821ed6e80627b8769d170a293862f9fc60825226'] as Commit;
+      final masterTree = repo[masterHead.tree.sha] as Tree;
+      expect(
+        masterTree.entries.any((e) => e.name == 'another_feature_file'),
+        false,
+      );
+
+      repo.checkout(refName: 'refs/heads/feature');
+      final featureHead =
+          repo['5aecfa0fb97eadaac050ccb99f03c3fb65460ad4'] as Commit;
+      final featureTree = repo[featureHead.tree.sha] as Tree;
+      final repoHead = repo.head;
+      expect(repoHead.target.sha, featureHead.id.sha);
+      expect(repo.status, isEmpty);
+      expect(
+        featureTree.entries.any((e) => e.name == 'another_feature_file'),
+        true,
+      );
+
+      repoHead.free();
+      featureTree.free();
+      featureHead.free();
+      masterTree.free();
+      masterHead.free();
+    });
+
+    test('successfully checkouts with alrenative directory', () {
+      final altDir = '${Directory.systemTemp.path}/alt_dir';
+      // making sure there is no directory
+      if (Directory(altDir).existsSync()) {
+        Directory(altDir).deleteSync(recursive: true);
+      }
+      Directory(altDir).createSync();
+      expect(Directory(altDir).listSync().length, 0);
+
+      repo.checkout(refName: 'refs/heads/feature', directory: altDir);
+      expect(Directory(altDir).listSync().length, isNot(0));
+
+      Directory(altDir).deleteSync(recursive: true);
+    });
+
+    test('successfully checkouts file with provided path', () {
+      expect(repo.status, isEmpty);
+      repo.checkout(
+        refName: 'refs/heads/feature',
+        paths: ['another_feature_file'],
+      );
+      expect(repo.status, {'another_feature_file': GitStatus.indexNew.value});
+    });
+  });
+}