Add tests for math rendering and interactive scenes; update navigation and viewport handling

- Updated `lab.spec.ts` to navigate directly to the field lesson.
- Created `math.spec.ts` with tests for math rendering, error checking, and responsive design.
- Added `test4.spec.ts` for interactive scenes, ensuring all questions are functional and accessible.
- Modified `vite.config.ts` to keep original question/answer links navigable in production.

1 files changed, 118 insertions, 0 deletions

diff --git a/tests/test4.spec.ts b/tests/test4.spec.ts
new file mode 100644
index 0000000..3e6a3b5
--- /dev/null
+++ b/tests/test4.spec.ts
@@ -0,0 +1,118 @@
+import { test, expect, type Page } from '@playwright/test';
+
+async function read(page: Page, label: string) {
+  return Number((await page.getByLabel(label, { exact: true }).innerText()).replaceAll(',', ''));
+}
+
+test('six original test questions have interactive scenes and every answer part', async ({ page }) => {
+  const errors: string[] = [];
+  page.on('pageerror', e => errors.push(e.message));
+  await page.goto('/');
+  const ids = ['work', 'conservation', 'central', 'assembly', 'uniform', 'dipole'];
+  const parts = [1, 1, 2, 2, 2, 3];
+  await expect(page.getByRole('tab')).toHaveCount(6);
+  for (let i = 0; i < ids.length; i++) {
+    await page.getByRole('tab').nth(i).click();
+    await expect(page).toHaveURL(new RegExp(`#test-${ids[i]}$`));
+    await expect(page.locator('#test-question')).not.toBeEmpty();
+    await expect(page.locator('#solution details')).toHaveCount(parts[i]);
+    await page.locator('#solution summary').first().click();
+    await expect(page.locator('#solution details[open] .derivation')).toBeVisible();
+    await expect(page.locator('#measurements')).not.toContainText('Undefined');
+    await expect(page.locator('canvas').first()).toBeVisible();
+    // Check actual rendered pixels, including scenes constructed after hash navigation.
+    await expect.poll(() => page.locator('#viewport > canvas').evaluate(canvas => new Promise<number>(resolve => {
+      requestAnimationFrame(() => requestAnimationFrame(() => {
+        const small = document.createElement('canvas'); small.width = 80; small.height = 60;
+        const context = small.getContext('2d')!;
+        context.drawImage(canvas as HTMLCanvasElement, 0, 0, 80, 60);
+        const data = context.getImageData(0, 0, 80, 60).data;
+        const colours = new Set<number>();
+        for (let k = 0; k < data.length; k += 4) colours.add((data[k] << 16) | (data[k + 1] << 8) | data[k + 2]);
+        resolve(colours.size);
+      }));
+    }))).toBeGreaterThan(12);
+  }
+  expect(errors).toEqual([]);
+});
+
+test('path changes preserve work while signed charge and angle change it', async ({ page }) => {
+  await page.goto('/#test-work');
+  const initial = await read(page, 'Field work a → b');
+  await page.getByLabel('Path shape', { exact: true }).selectOption('curved');
+  expect(await read(page, 'Field work a → b')).toBe(initial);
+  await page.getByRole('slider', { name: 'Moving charge q₀', exact: true }).fill('-2');
+  expect(await read(page, 'Field work a → b')).toBe(-initial);
+  await page.goto('/#test-uniform');
+  await page.getByRole('slider', { name: 'Displacement angle α', exact: true }).fill('90');
+  expect(Math.abs(await read(page, 'Field work a → b'))).toBeLessThan(1e-10);
+});
+
+test('energy conservation, infinity and dipole equilibrium stay physically consistent', async ({ page }) => {
+  await page.goto('/#test-conservation');
+  const total = await read(page, 'Total K + U');
+  await page.getByRole('slider', { name: 'Journey progress', exact: true }).fill('100');
+  expect(await read(page, 'Total K + U')).toBe(total);
+  expect(await read(page, 'Kinetic energy K')).toBeGreaterThan(0);
+  await page.goto('/#test-central');
+  await page.getByLabel('Destination b', { exact: true }).selectOption('infinity');
+  expect(await read(page, 'Potential energy Uᵦ')).toBe(0);
+  await expect(page.locator('#observation')).toContainText('infinity');
+  await page.goto('/#test-dipole');
+  await page.getByRole('slider', { name: 'Final angle θᵦ', exact: true }).fill('0');
+  await page.getByRole('slider', { name: 'Rotation progress', exact: true }).fill('100');
+  expect(await read(page, 'Potential energy U')).toBeLessThan(0);
+  expect(await read(page, 'Torque τz')).toBe(0);
+  await expect(page.locator('#observation')).toContainText('stable');
+});
+
+test('assembly adds q₀ without double counting and the prediction can be revealed', async ({ page }) => {
+  await page.goto('/#test-assembly');
+  await page.getByLabel('Assembly stage', { exact: true }).selectOption('3');
+  const base = await read(page, 'Energy of current assembly');
+  await page.getByLabel('Assembly stage', { exact: true }).selectOption('4');
+  expect(await read(page, 'Energy of current assembly')).toBeCloseTo(base + await read(page, 'Additional energy ΔU₀'), 1);
+  await expect(page.locator('#prediction-answer')).toBeHidden();
+  await page.getByRole('button', { name: 'Reveal explanation' }).click();
+  await expect(page.locator('#prediction-answer')).toBeVisible();
+});
+
+test('collection navigation retains settings, works with history, and fits mobile', async ({ page }) => {
+  await page.goto('/#test-dipole');
+  await page.getByRole('slider', { name: 'Final angle θᵦ', exact: true }).fill('180');
+  await page.getByRole('link', { name: 'All experiments', exact: true }).click();
+  await expect(page.getByRole('tab')).toHaveCount(8);
+  await page.goBack();
+  await expect(page.getByRole('slider', { name: 'Final angle θᵦ', exact: true })).toHaveValue('180');
+  await page.getByRole('button', { name: 'Reset experiment' }).click();
+  await expect(page.getByRole('slider', { name: 'Final angle θᵦ', exact: true })).toHaveValue('15');
+  await page.setViewportSize({ width: 390, height: 844 });
+  await expect(page.locator('canvas')).toBeVisible();
+  expect(await page.evaluate(() => document.documentElement.scrollWidth <= innerWidth)).toBe(true);
+});
+
+test('next question returns a mobile learner to the new heading', async ({ page }) => {
+  await page.setViewportSize({ width: 390, height: 844 });
+  await page.goto('/#test-work');
+  await page.getByRole('link', { name: 'Next question →', exact: true }).click();
+  await expect(page).toHaveURL(/#test-conservation$/);
+  await expect(page.getByRole('heading', { name: 'Where does the energy go?' })).toBeInViewport();
+  await expect(page.locator('#lesson-title')).toBeFocused();
+});
+
+test('test answers and controls remain accessible without WebGL', async ({ page }) => {
+  await page.addInitScript(() => {
+    const original = HTMLCanvasElement.prototype.getContext;
+    HTMLCanvasElement.prototype.getContext = function (type: string, ...args: unknown[]) {
+      if (type.startsWith('webgl')) return null;
+      return original.call(this, type as '2d', ...args as []) as never;
+    } as typeof original;
+  });
+  await page.goto('/#test-dipole');
+  await expect(page.getByRole('alert')).toContainText('WebGL');
+  await page.getByRole('slider', { name: 'Rotation progress', exact: true }).fill('100');
+  expect(await read(page, 'Potential energy U')).toBeLessThan(0);
+  await page.locator('#solution summary').last().click();
+  await expect(page.locator('#solution details[open] math').first()).toBeAttached();
+  await expect(page.locator('#solution details[open] .katex-error')).toHaveCount(0);
+});