fix(compare): show SSR data on refresh; drop dead per-page comparison fetch

Refresh bug: on mount the basket is empty for a beat before it hydrates from the URL. The fetch effect nulled comparisonData on that transient empty urnKey, then the one-shot 'SSR covers it' skip suppressed the refetch — leaving the page blank on reload. The effect is now gated on isInitialized, never blanks on empty (the render already shows the empty state when nothing is selected), and decides fetch-vs-skip by whether it already holds each requested school's data (SSR or a prior fetch). Perf: useComparison ran a useSWR('/api/compare') whose result nothing consumed — dead weight that fired on every page (Navigation + Toast are global) whenever the basket was non-empty, and duplicated ComparisonView's own fetch on the compare page. Removed; the hook now exposes basket state only. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_0146VHeLAWjDVE2B5uU67jCB
2026-07-14 22:34:20 +01:00
parent 8e4ee64140
commit 43a2c4a6bc
3 changed files with 111 additions and 60 deletions
@@ -0,0 +1,82 @@
+/**
+ * Regression: on refresh, the compare page must show the SSR-rendered data.
+ *
+ * The basket hydrates from the URL a beat after mount (selectedSchools is
+ * empty for the first render), so the fetch effect must not blank the
+ * SSR payload during that window — and must not refetch data the server
+ * already provided.
+ */
+
+import { render, screen, waitFor } from '@testing-library/react';
+
+import { ComparisonView } from '@/components/ComparisonView';
+import { ComparisonProvider } from '@/context/ComparisonProvider';
+import type { ComparisonData, School } from '@/lib/types';
+
+const fetchComparison = jest.fn();
+jest.mock('@/lib/api', () => ({
+  fetchComparison: (...args: unknown[]) => fetchComparison(...args),
+}));
+jest.mock('@/lib/analytics', () => ({ track: jest.fn() }));
+
+function school(urn: number, name: string): School {
+  return {
+    urn,
+    school_name: name,
+    local_authority: 'Testshire',
+    school_type: 'Community school',
+    rwm_expected_pct: 80,
+    phase: 'Primary',
+  } as School;
+}
+
+function data(urn: number, name: string): ComparisonData {
+  return {
+    school_info: school(urn, name),
+    yearly_data: [{ year: 202425, rwm_expected_pct: 80 }] as ComparisonData['yearly_data'],
+    ofsted: null,
+    census: null,
+    admissions: null,
+    admissions_history: [],
+    deprivation: null,
+  };
+}
+
+const INITIAL_DATA = {
+  '100': data(100, 'Alpha Primary'),
+  '200': data(200, 'Beta Primary'),
+};
+
+beforeEach(() => {
+  fetchComparison.mockReset();
+});
+
+test('renders SSR data on refresh without wiping it or refetching', async () => {
+  render(
+    <ComparisonProvider>
+      <ComparisonView
+        initialData={INITIAL_DATA}
+        initialNationalAverages={{
+          year: 202425,
+          primary: { rwm_expected_pct: 62 },
+          secondary: {},
+          by_year: [],
+        }}
+        initialBenchmarks={undefined}
+        initialUrns={[100, 200]}
+        metrics={[]}
+        selectedMetric="rwm_expected_pct"
+      />
+    </ComparisonProvider>,
+  );
+
+  // Both SSR-provided schools appear (data was not blanked during hydration)
+  await waitFor(() => {
+    expect(screen.getAllByText('Alpha Primary').length).toBeGreaterThan(0);
+  });
+  expect(screen.getAllByText('Beta Primary').length).toBeGreaterThan(0);
+  expect(screen.getByRole('heading', { name: 'At a glance' })).toBeInTheDocument();
+
+  // …and the client never refetched data the server already rendered.
+  expect(fetchComparison).not.toHaveBeenCalled();
+});