Merge pull request 'fix(tests): the error-handling suite would not compile, and nothing local said so (#307)' (#323) from fix/307-integration-typecheck into main

Reviewed-on: #323

backend/package.json

@@ -8,6 +8,7 @@
   },
   "scripts": {
     "build": "tsc",
+    "typecheck:tests": "tsc -p tsconfig.test.json --noEmit",
     "lint": "eslint src scripts tests",
     "start": "node dist/server.js",
     "dev": "tsx watch src/server.ts",

backend/tests/integration/errorHandling.integration.test.ts

@@ -34,7 +34,13 @@ const DB_FAILURE = 'invalid input syntax for type integer while reading items';
  * spy is not sensitive to how the module is transpiled.
  */
 function failNextQuery() {
-  return jest.spyOn(pool, 'query').mockRejectedValueOnce(new Error(DB_FAILURE));
+  // `as never` is the type system, not a shortcut. `pg` declares `query` with
+  // several overloads, and `jest.spyOn` resolves the mock's argument against
+  // the last of them, whose parameter list is empty — so the inferred type for
+  // a rejection value is `never` and nothing can be assigned to it. Rejecting
+  // is what all of the overloads do on failure; the cast only says which one to
+  // check against.
+  return jest.spyOn(pool, 'query').mockRejectedValueOnce(new Error(DB_FAILURE) as never);
 }
 
 describe('unexpected route failures', () => {