feat(tag): add bindings and api

test/tag_test.dart

@@ -0,0 +1,91 @@
+import 'dart:io';
+
+import 'package:test/test.dart';
+import 'package:libgit2dart/libgit2dart.dart';
+import 'helpers/util.dart';
+
+void main() {
+  late Repository repo;
+  late Tag tag;
+  final tmpDir = '${Directory.systemTemp.path}/tag_testrepo/';
+  const tagSHA = 'f0fdbf506397e9f58c59b88dfdd72778ec06cc0c';
+
+  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);
+    tag = Tag.lookup(repo, Oid.fromSHA(repo, tagSHA));
+  });
+
+  tearDown(() async {
+    tag.free();
+    repo.free();
+    await Directory(tmpDir).delete(recursive: true);
+  });
+
+  group('Tag', () {
+    test('successfully initializes tag from provided Oid', () {
+      expect(tag, isA<Tag>());
+    });
+
+    test('returns correct values', () {
+      final signature = Signature.create(
+        name: 'Aleksey Kulikov',
+        email: 'skinny.mind@gmail.com',
+        time: 1630599723,
+        offset: 180,
+      );
+      final target = tag.target;
+      final tagger = tag.tagger;
+
+      expect(tag.id.sha, tagSHA);
+      expect(tag.name, 'v0.2');
+      expect(tag.message, 'annotated tag\n');
+      expect(target.message, 'add subdirectory file\n');
+      expect(tagger, signature);
+
+      signature.free();
+      target.free();
+    });
+
+    test('successfully creates new tag', () {
+      final signature = Signature.create(
+        name: 'Author',
+        email: 'author@email.com',
+        time: 1234,
+      );
+      const tagName = 'tag';
+      final target =
+          Oid.fromSHA(repo, 'f17d0d48eae3aa08cecf29128a35e310c97b3521');
+      const message = 'init tag\n';
+
+      final oid = Tag.create(
+        repository: repo,
+        tagName: tagName,
+        target: target,
+        targetType: GitObject.commit,
+        tagger: signature,
+        message: message,
+      );
+
+      final newTag = Tag.lookup(repo, oid);
+      final tagger = newTag.tagger;
+      final newTagTarget = newTag.target;
+
+      expect(newTag.id.sha, '131a5eb6b7a880b5096c550ee7351aeae7b95a42');
+      expect(newTag.name, tagName);
+      expect(newTag.message, message);
+      expect(tagger, signature);
+      expect(newTagTarget.id, target);
+
+      newTag.free();
+      newTagTarget.free();
+      signature.free();
+    });
+  });
+}