feat(core): add Electron runtime, services, and app composition

src/core/services/mpv-render-metrics.test.ts

@@ -0,0 +1,25 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { MpvSubtitleRenderMetrics } from '../../types';
+import {
+  applyMpvSubtitleRenderMetricsPatch,
+  DEFAULT_MPV_SUBTITLE_RENDER_METRICS,
+} from './mpv-render-metrics';
+
+const BASE: MpvSubtitleRenderMetrics = {
+  ...DEFAULT_MPV_SUBTITLE_RENDER_METRICS,
+};
+
+test('applyMpvSubtitleRenderMetricsPatch returns unchanged on empty patch', () => {
+  const { next, changed } = applyMpvSubtitleRenderMetricsPatch(BASE, {});
+  assert.equal(changed, false);
+  assert.deepEqual(next, BASE);
+});
+
+test('applyMpvSubtitleRenderMetricsPatch reports changed when patch modifies value', () => {
+  const { next, changed } = applyMpvSubtitleRenderMetricsPatch(BASE, {
+    subPos: 95,
+  });
+  assert.equal(changed, true);
+  assert.equal(next.subPos, 95);
+});