feat: scaffold Flask + React app with schema and JSON error handling

Claude-Session: https://claude.ai/code/session_01M9MLit5Ko3X4s7rzC5Kv7X

backend/tests/support.py

@@ -0,0 +1,58 @@
+import os
+import unittest
+
+import psycopg2
+
+from app import app
+
+HTTPS = "https://localhost"  # the session cookie is Secure
+
+
+def db_execute(sql: str, params: tuple = ()) -> list[tuple]:
+    conn = psycopg2.connect(os.environ["DATABASE_URL"])
+    try:
+        with conn, conn.cursor() as cur:
+            cur.execute(sql, params)
+            return cur.fetchall() if cur.description else []
+    finally:
+        conn.close()
+
+
+class ApiTestCase(unittest.TestCase):
+    def setUp(self):
+        if not os.environ["DATABASE_URL"].endswith("/books_test"):
+            raise RuntimeError("Refusing to truncate a database that is not books_test")
+        db_execute("TRUNCATE users, sessions, books, notes RESTART IDENTITY CASCADE")
+        self.client = app.test_client()
+
+    def call(self, method, path, json=None, client=None):
+        kwargs = {"method": method, "base_url": HTTPS}
+        if json is not None:
+            kwargs["json"] = json
+        elif method != "GET":
+            kwargs["content_type"] = "application/json"
+        return (client or self.client).open(path, **kwargs)
+
+    def register(self, username="alice", password="correct horse battery", client=None):
+        response = self.call("POST", "/api/auth/register", {"username": username, "password": password}, client)
+        self.assertEqual(response.status_code, 201, response.get_json())
+        return response
+
+    def other_user(self, username="bob"):
+        client = app.test_client()
+        self.register(username, client=client)
+        return client
+
+    def genre_id(self, name: str) -> int:
+        return db_execute("SELECT id FROM genres WHERE name = %s", (name,))[0][0]
+
+    def create_book(self, client=None, **overrides) -> dict:
+        payload = {
+            "title": "Dune",
+            "author": "Frank Herbert",
+            "genre_id": self.genre_id("Science Fiction"),
+            "total_pages": 412,
+        } | overrides
+        response = self.call("POST", "/api/books", payload, client)
+        self.assertEqual(response.status_code, 201, response.get_json())
+        return response.get_json()