test: cover built-in theme preset ordering

tests/theme-presets.test.mjs

@@ -0,0 +1,42 @@
+import assert from 'node:assert/strict';
+import { readFile } from 'node:fs/promises';
+import test from 'node:test';
+
+const source = await readFile(
+  new URL('../src/lib/components/SettingsPanel.svelte', import.meta.url),
+  'utf8'
+);
+const initialization = source.match(
+  /(const\s+themePresets\s*=\s*\[[\s\S]*?\];)[\s\S]*?(?=\bconst\s+accentPresets\s*=)/
+);
+assert.ok(initialization, 'theme presets initialization was not found');
+
+// Evaluate only the trusted repository declaration and its initialization code.
+const unsorted = new Function(`${initialization[1]}\nreturn themePresets;`)();
+const presets = new Function(`${initialization[0]}\nreturn themePresets;`)();
+
+test('pins System, Light, and Dark in that exact order', () => {
+  assert.deepEqual(presets.slice(0, 3).map(({ id, label }) => ({ id, label })), [
+    { id: 'system', label: 'System' },
+    { id: 'light', label: 'Light' },
+    { id: 'dark', label: 'Dark' }
+  ]);
+});
+
+test('orders remaining built-in labels alphabetically, including Rosé Pine', () => {
+  const labels = presets.slice(3).map((preset) => preset.label);
+  assert.ok(labels.includes('Rosé Pine'));
+  assert.deepEqual(labels, [...labels].sort());
+});
+
+test('preserves every theme ID, label, and color without duplicates', () => {
+  assert.equal(presets.length, unsorted.length);
+  for (const themes of [unsorted, presets]) {
+    assert.equal(new Set(themes.map((preset) => preset.id)).size, themes.length);
+    assert.equal(new Set(themes.map((preset) => preset.label)).size, themes.length);
+  }
+  assert.deepEqual(
+    Object.fromEntries(presets.map((preset) => [preset.id, preset])),
+    Object.fromEntries(unsorted.map((preset) => [preset.id, preset]))
+  );
+});