feat: collapse diff files by default (#270)

* feat: collapse diff files by default

* feat: expand source diffs by default

---------

Co-authored-by: wangqiong <wangqiong@yy.com>

tests/diff-view-collapse.spec.tsx

@@ -0,0 +1,59 @@
+// @vitest-environment jsdom
+import { afterEach, describe, expect, it } from 'vitest'
+import { createElement } from 'react'
+import { createRoot, type Root } from 'react-dom/client'
+import { act } from 'react-dom/test-utils'
+import { DiffView } from '../src/client/DiffView.tsx'
+
+;(globalThis as Record<string, unknown>).IS_REACT_ACT_ENVIRONMENT = true
+
+const diff = [
+  'diff --git a/src/a.ts b/src/a.ts',
+  '--- a/src/a.ts',
+  '+++ b/src/a.ts',
+  '@@ -1 +1 @@',
+  '-old-a',
+  '+new-a',
+  'diff --git a/tests/b.spec.ts b/tests/b.spec.ts',
+  '--- a/tests/b.spec.ts',
+  '+++ b/tests/b.spec.ts',
+  '@@ -1 +1 @@',
+  '-old-b',
+  '+new-b',
+  'diff --git a/README.md b/README.md',
+  '--- a/README.md',
+  '+++ b/README.md',
+  '@@ -1 +1 @@',
+  '-old-doc',
+  '+new-doc',
+].join('\n')
+
+afterEach(() => { document.body.innerHTML = '' })
+
+describe('DiffView file folding', () => {
+  it('expands source by default while tests and docs stay collapsed', () => {
+    const container = document.createElement('div')
+    document.body.append(container)
+    const root: Root = createRoot(container)
+    try {
+      act(() => { root.render(createElement(DiffView, { diff })) })
+      const headers = [...container.querySelectorAll<HTMLButtonElement>('button[aria-expanded]')]
+      expect(headers).toHaveLength(3)
+      expect(headers.map(header => header.getAttribute('aria-expanded'))).toEqual(['true', 'false', 'false'])
+      expect(container.textContent).toContain('new-a')
+      expect(container.textContent).not.toContain('new-b')
+      expect(container.textContent).not.toContain('new-doc')
+
+      act(() => { headers[1]!.click() })
+      expect(headers[1]!.getAttribute('aria-expanded')).toBe('true')
+      expect(container.textContent).toContain('new-b')
+
+      act(() => { headers[0]!.click() })
+      expect(headers[0]!.getAttribute('aria-expanded')).toBe('false')
+      expect(container.textContent).not.toContain('new-a')
+    } finally {
+      act(() => { root.unmount() })
+      container.remove()
+    }
+  })
+})