Improve test coverance and fixes according to tests

app/tests/test_services.py

@@ -0,0 +1,106 @@
+import pytest
+from unittest.mock import patch
+
+from app.services import url_service
+from app.db.models import URL
+
+
+def test_create_short_url_creates_new(db_session):
+    short_url = url_service.create_short_url(
+        db_session,
+        "https://new-url.com",
+    )
+
+    assert short_url.startswith("http://")
+
+    entry = db_session.query(URL).first()
+    assert entry is not None
+    assert entry.original_url == "https://new-url.com"
+
+
+def test_create_short_url_returns_existing(db_session):
+    first = url_service.create_short_url(
+        db_session,
+        "https://duplicate.com",
+    )
+
+    second = url_service.create_short_url(
+        db_session,
+        "https://duplicate.com",
+    )
+
+    assert first == second
+    assert db_session.query(URL).count() == 1
+
+
+def test_create_short_url_collision_failure(db_session):
+    with patch(
+        "app.services.url_service.generate_short_code",
+        return_value="fixedcode",
+    ):
+        # First insert works
+        url_service.create_short_url(db_session, "https://a.com")
+
+        # Force collision repeatedly
+        with pytest.raises(RuntimeError):
+            url_service.create_short_url(db_session, "https://b.com")
+
+
+def test_get_original_url_success(db_session):
+    short_url = url_service.create_short_url(
+        db_session,
+        "https://lookup.com",
+    )
+    code = short_url.split("/")[-1]
+
+    original = url_service.get_original_url(db_session, code)
+
+    assert original == "https://lookup.com"
+
+
+def test_get_original_url_not_found(db_session):
+    result = url_service.get_original_url(db_session, "missing")
+    assert result is None
+
+
+def test_increment_clicks_success(db_session):
+    short_url = url_service.create_short_url(
+        db_session,
+        "https://click-test.com",
+    )
+    code = short_url.split("/")[-1]
+
+    success = url_service.increment_clicks(db_session, code)
+
+    assert success is True
+
+    entry = db_session.query(URL).first()
+    assert entry.clicks == 1
+    assert entry.last_accessed is not None
+
+
+def test_increment_clicks_not_found(db_session):
+    result = url_service.increment_clicks(db_session, "missing")
+    assert result is False
+
+
+def test_get_stats_success(db_session):
+    short_url = url_service.create_short_url(
+        db_session,
+        "https://stats.com",
+    )
+    code = short_url.split("/")[-1]
+
+    url_service.increment_clicks(db_session, code)
+
+    stats = url_service.get_stats(db_session, code)
+
+    assert stats is not None
+    assert stats["original_url"] == "https://stats.com"
+    assert stats["clicks"] == 1
+    assert stats["created_at"] is not None
+
+
+def test_get_stats_not_found(db_session):
+    stats = url_service.get_stats(db_session, "missing")
+    assert stats is None