🐛 fix(frontend): Playwright now detects health endpoint failures (was silently passing) (#32)

User caught silent regression: existing test only asserted dashboard visibility, which is also true on the error branch. New tests assert healthy state + new regression test mocks /api/healthz to 502.

Co-authored-by: Gabriel Radureau <arcodange@gmail.com>
Co-committed-by: Gabriel Radureau <arcodange@gmail.com>

frontend/tests/e2e/health.spec.ts

@@ -1,9 +1,37 @@
 import { test, expect } from '@playwright/test'
 
-test('home page loads and shows server health info', async ({ page }) => {
+test('home page loads and shows healthy server state', async ({ page }) => {
   await page.goto('/')
   await expect(page.getByTestId('health-dashboard')).toBeVisible()
   const heading = page.getByRole('heading', { name: /dance-lessons-coach/i })
   await expect(heading).toBeVisible()
+
+  // Assert the dashboard is in HEALTHY state, not an error state.
+  // The dashboard renders an "Error loading health: ..." paragraph when /api/healthz
+  // is unreachable (Go backend not running, proxy misconfigured, endpoint removed,
+  // etc.). Without these assertions the test would falsely PASS even when the
+  // dashboard shows the error UI - regression observed 2026-05-03 (Go backend
+  // not running locally → page renders the error, Playwright PASSES).
+  await expect(page.getByTestId('health-info')).toBeVisible()
+  await expect(page.getByTestId('health-status')).toHaveText('healthy')
+  await expect(page.getByText(/Error loading health/i)).not.toBeVisible()
+
   await page.screenshot({ path: 'tests/e2e/screenshots/home-page-loads-and-shows-server-health-info.png', fullPage: true })
 })
+
+// Regression spec: documents the expected error UX so we don't ship a silent failure.
+// Routes /api/healthz to a 502 mock so the test is reproducible regardless of backend.
+test('home page surfaces health endpoint errors visibly', async ({ page }) => {
+  await page.route('**/api/healthz', (route) => {
+    route.fulfill({
+      status: 502,
+      contentType: 'application/json',
+      body: JSON.stringify({ error: 'simulated_backend_down' }),
+    })
+  })
+  await page.goto('/')
+  await expect(page.getByTestId('health-dashboard')).toBeVisible()
+  await expect(page.getByText(/Error loading health/i)).toBeVisible()
+  await expect(page.getByTestId('health-info')).not.toBeVisible()
+  await page.screenshot({ path: 'tests/e2e/screenshots/home-page-surfaces-health-endpoint-errors-visibly.png', fullPage: true })
+})