test(chapter): PKG-CHAPTER-02 cover behavior and optional factory types

packages/artplayer-plugin-chapter/README.md

@@ -6,6 +6,36 @@ chapter plugin for ArtPlayer
 
 [https://artplayer.org](https://artplayer.org/?libs=./uncompiled/artplayer-plugin-chapter/index.js&example=chapter)
 
+## API
+
+```js
+import artplayerPluginChapter from 'artplayer-plugin-chapter'
+
+const plugin = artplayerPluginChapter({
+  chapters: [{ start: 0, end: Infinity, title: 'Introduction' }],
+})
+// Pass plugin to Artplayer's plugins array. Options may also be omitted.
+```
+
+The registered name is `artplayerPluginChapter`. After metadata loads, use
+`art.plugins.artplayerPluginChapter.update({ chapters })` to replace the chapters, or
+`update({})` to clear them. Update is synchronous and requires an options object.
+Chapter times are seconds; ranges must not overlap. `Infinity` as an end value uses the current duration.
+
+The existing implementation sorts and fills the supplied array in place and replaces its Infinity end
+values. Pass a fresh array when you need to retain the original configuration. After switching media,
+call update with chapters appropriate to the new duration; initialization listens to metadata once.
+
+## Maintenance
+
+The implementation is currently in `src/index.js`, styles in `src/style.less`, and public declarations
+in `types/artplayer-plugin-chapter.d.ts`. Its migration contracts and known defects are recorded in
+[the chapter contract](../../refactor/baselines/chapter-contract.md).
+
+Run `yarn test:browser chapter.spec.js` for published/current plugin behavior on the published core.
+Run `yarn typecheck` and `yarn test:baseline` for strict consumer checks, including optional factory
+arguments and invalid data. `yarn build:ts` regenerates the online editor declarations.
+
 ## License
 
 MIT © Harvey Zhao

packages/artplayer-plugin-chapter/types/artplayer-plugin-chapter.d.ts

@@ -15,6 +15,6 @@ interface Result {
   update: (option: Option) => void
 }
 
-declare const artplayerPluginChapter: (option: Option) => (art: Artplayer) => Result
+declare const artplayerPluginChapter: (option?: Option) => (art: Artplayer) => Result
 
 export default artplayerPluginChapter