test+ci: add regression tests and GitHub Actions workflow

tests/test_serialization.py

@@ -0,0 +1,22 @@
+from __future__ import annotations
+
+from twitter_cli.serialization import tweet_from_dict, tweet_to_dict, tweets_from_json, tweets_to_json
+
+
+def test_tweet_roundtrip_dict(tweet_factory) -> None:
+    tweet = tweet_factory("42")
+    payload = tweet_to_dict(tweet)
+    restored = tweet_from_dict(payload)
+
+    assert restored.id == tweet.id
+    assert restored.author.screen_name == tweet.author.screen_name
+    assert restored.metrics.likes == tweet.metrics.likes
+
+
+def test_tweets_json_roundtrip(tweet_factory) -> None:
+    tweets = [tweet_factory("1"), tweet_factory("2", lang="zh")]
+    raw = tweets_to_json(tweets)
+    restored = tweets_from_json(raw)
+
+    assert [tweet.id for tweet in restored] == ["1", "2"]
+    assert restored[1].lang == "zh"