test: data router, one render helper, fetchRoutes in every test

src/test/fetchRoutes.js

@@ -1,20 +1,27 @@
-import {vi} from 'vitest';
+import {onTestFinished, vi} from 'vitest';
 
 export const json = (status, body) => ({ok: status >= 200 && status < 300, status, json: async () => body});
 
 /**
  * A fetch mock that answers by method and path, e.g. `'GET /api/users/me'`. The path starts at `/api/` (the base URL
  * is not set in tests) and leaves out the query. A value is an answer or `(url, init) => answer`. Any other request
- * throws, so a test cannot pass on a request it did not expect.
+ * rejects, and the test fails at its end even when the page catches the error.
  * Sets `globalThis.fetch` and returns the mock.
  */
 export function fetchRoutes(routes) {
+    const unknown = [];
     const mock = vi.fn(async (url, init) => {
         const key = `${init?.method ?? 'GET'} ${new URL(url, 'http://x').pathname.replace(/^.*?(?=\/api\/)/, '')}`;
-        if (!(key in routes)) throw new Error(`no route ${key}`);
+        if (!(key in routes)) {
+            unknown.push(key);
+            throw new Error(`no route ${key}`);
+        }
         const answer = routes[key];
         return typeof answer === 'function' ? answer(url, init) : answer;
     });
     globalThis.fetch = mock;
+    onTestFinished(() => {
+        if (unknown.length) throw new Error(`requests without a route: ${[...new Set(unknown)].join(', ')}`);
+    });
     return mock;
 }