test+ci: add regression tests and GitHub Actions workflow

tests/test_cli.py

@@ -0,0 +1,28 @@
+from __future__ import annotations
+
+from click.testing import CliRunner
+
+from twitter_cli.cli import cli
+from twitter_cli.models import UserProfile
+from twitter_cli.serialization import tweets_to_json
+
+
+def test_cli_user_command_works_with_client_factory(monkeypatch) -> None:
+    class FakeClient:
+        def fetch_user(self, screen_name: str) -> UserProfile:
+            return UserProfile(id="1", name="Alice", screen_name=screen_name)
+
+    monkeypatch.setattr("twitter_cli.cli._get_client", lambda: FakeClient())
+    runner = CliRunner()
+    result = runner.invoke(cli, ["user", "alice"])
+    assert result.exit_code == 0
+
+
+def test_cli_feed_json_input_path(tmp_path, tweet_factory) -> None:
+    json_path = tmp_path / "tweets.json"
+    json_path.write_text(tweets_to_json([tweet_factory("1")]), encoding="utf-8")
+
+    runner = CliRunner()
+    result = runner.invoke(cli, ["feed", "--input", str(json_path), "--json"])
+    assert result.exit_code == 0
+    assert '"id": "1"' in result.output