feat: add like/unlike toggle on blog posts with per-user tracking

- PostLike domain entity (post_id, liked_by) with BaseEntity integration
- Post entity: add like_count field (default 0) and to_dict serialization
- PostRepository interface: add get_like, add_like, remove_like methods
- TogglePostLikeUseCase: toggle logic (like → unlike, unlike → like)
- PostResponseDTO/PostResponseSchema: add like_count field
- PostLikeORM model with FK to posts and cascade delete
- SQLAlchemyPostRepository: implement like query/add/remove with ORM mapping
- DI provider registration for TogglePostLikeUseCase
- API endpoint POST /api/v1/posts/{id}/like (auth required)
- Unit tests: PostLike entity, Post.like_count, TogglePostLikeUseCase (7 tests)
- API tests: POST /api/v1/posts/{id}/like (4 tests)
- Test model files: FEATURE_LIKES.md, TEST_MODEL.md updated

tests/api/test_likes.py

@@ -0,0 +1,94 @@
+"""API tests for post like/unlike toggle.
+
+This module tests the POST /api/v1/posts/{post_id}/like endpoint covering
+authenticated toggle on, toggle off, guest access, and not-found scenarios.
+"""
+
+from typing import Any
+
+from fastapi.testclient import TestClient
+
+from tests.api.conftest import API_PREFIX
+
+
+class TestLikePost:
+    """Tests for POST /api/v1/posts/{post_id}/like — toggle like on a post."""
+
+    def test_like_post_authenticated(
+        self,
+        client: TestClient,
+        user_headers: dict[str, str],
+        created_post: dict[str, Any],
+    ) -> None:
+        """Test liking a post as authenticated user returns like_count=1.
+
+        TC-API-114: Positive — authenticated like toggle on.
+        """
+        post_id = created_post["id"]
+
+        response = client.post(
+            f"{API_PREFIX}/{post_id}/like",
+            headers=user_headers,
+        )
+        assert response.status_code == 200
+        data = response.json()
+        assert data["like_count"] == 1
+        assert data["id"] == post_id
+
+    def test_unlike_post_authenticated(
+        self,
+        client: TestClient,
+        user_headers: dict[str, str],
+        created_post: dict[str, Any],
+    ) -> None:
+        """Test unliking a post that was already liked returns like_count=0.
+
+        TC-API-115: Positive — authenticated like toggle off.
+        """
+        post_id = created_post["id"]
+
+        client.post(f"{API_PREFIX}/{post_id}/like", headers=user_headers)
+
+        response = client.post(
+            f"{API_PREFIX}/{post_id}/like",
+            headers=user_headers,
+        )
+        assert response.status_code == 200
+        data = response.json()
+        assert data["like_count"] == 0
+        assert data["id"] == post_id
+
+    def test_like_post_as_guest(
+        self,
+        client: TestClient,
+        guest_headers: dict[str, str],
+        created_post: dict[str, Any],
+    ) -> None:
+        """Test liking a post as guest (inactive token) returns 401.
+
+        TC-API-116: Negative — guest/inactive token cannot like.
+        """
+        post_id = created_post["id"]
+        response = client.post(
+            f"{API_PREFIX}/{post_id}/like",
+            headers=guest_headers,
+        )
+        assert response.status_code == 401
+
+    def test_like_post_not_found(
+        self,
+        client: TestClient,
+        user_headers: dict[str, str],
+    ) -> None:
+        """Test liking a non-existent post returns 404.
+
+        TC-API-117: Negative — post not found.
+        """
+        fake_id = "00000000-0000-0000-0000-000000000000"
+        response = client.post(
+            f"{API_PREFIX}/{fake_id}/like",
+            headers=user_headers,
+        )
+        assert response.status_code == 404
+        error = response.json()
+        assert error["error"] == "NotFoundException"