test: pin school detail behaviour before refactor

14 characterization tests covering Ofsted (both OEIF and Report Card layouts),
KS2 results with the England delta, KS4 Attainment 8 / Progress 8 / EBacc,
all-through dual rendering, special-school comparison suppression (PR #70),
the admissions year/trend toggle, and conditional section rendering.

All rendering goes through renderSchoolDetail(), the single seam the
server/client split is allowed to change. The assertions must survive the
refactor unmodified.

Excludes __tests__/support from testMatch: it holds fixtures and helpers, not
suites, and the glob was failing them as empty test files.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

nextjs-app/__tests__/support/renderSchoolDetail.tsx

@@ -0,0 +1,43 @@
+/**
+ * The single seam between the characterization tests and the component tree.
+ *
+ * Task 7 of the server/client split rewrites the bodies of these functions to
+ * render the new shell + server-sections composition. Nothing else in the test
+ * suite may change — the characterization assertions passing unmodified across
+ * that rewrite is the proof that behaviour was preserved.
+ *
+ * National averages are currently fetched client-side via useEffect, so this
+ * helper stubs global.fetch. Once they arrive as a server-supplied prop the
+ * stub goes away; the tests use findBy* queries so they pass either way.
+ */
+
+import { render } from '@testing-library/react';
+import type { ReactNode } from 'react';
+import { SchoolDetailView } from '@/components/SchoolDetailView';
+import { SecondarySchoolDetailView } from '@/components/SecondarySchoolDetailView';
+import { ComparisonProvider } from '@/context/ComparisonProvider';
+import { nationalAveragesFixture } from './schoolFixtures';
+
+// Both views call useComparison(), which throws outside the provider. In the
+// app this wrapper comes from app/layout.tsx.
+function withProviders(ui: ReactNode) {
+  return <ComparisonProvider>{ui}</ComparisonProvider>;
+}
+
+function stubNationalAveragesFetch() {
+  global.fetch = jest.fn((url: any) =>
+    String(url).includes('national-averages')
+      ? Promise.resolve({ ok: true, json: () => Promise.resolve(nationalAveragesFixture) })
+      : Promise.resolve({ ok: false, json: () => Promise.resolve({}) }),
+  ) as unknown as typeof fetch;
+}
+
+export function renderSchoolDetail(fixture: any) {
+  stubNationalAveragesFetch();
+  return render(withProviders(<SchoolDetailView {...fixture} />));
+}
+
+export function renderSecondarySchoolDetail(fixture: any) {
+  stubNationalAveragesFetch();
+  return render(withProviders(<SecondarySchoolDetailView {...fixture} />));
+}