refactor(tests): decentralize monolithic unit.spec.ts and add state boundary tests (#141)

Co-authored-by: yukun.wu <yukun.wu@justcoglobal.com>

tests/file-types.spec.ts

@@ -0,0 +1,48 @@
+import { describe, expect, it } from 'vitest'
+import { isImageExt } from '../src/client/image-types.ts'
+import { extOf, languageKeyForExt } from '../src/client/lang.ts'
+import { isPdfExt } from '../src/client/pdf-types.ts'
+
+describe('editor language mapping', () => {
+  it('derives extensions from paths', () => {
+    expect(extOf('/a/b/main.tsx')).toBe('tsx')
+    expect(extOf('README.MD')).toBe('md')
+    expect(extOf('/a/b/.gitignore')).toBe('gitignore')
+    expect(extOf('noext')).toBe('')
+  })
+
+  it('maps common extensions to languages and falls back to plain text', () => {
+    expect(languageKeyForExt('tsx')).toBe('tsx')
+    expect(languageKeyForExt('js')).toBe('js')
+    expect(languageKeyForExt('py')).toBe('python')
+    expect(languageKeyForExt('yaml')).toBe('yaml')
+    expect(languageKeyForExt('sh')).toBe('shell')
+    expect(languageKeyForExt('md')).toBe('md')
+    expect(languageKeyForExt('cs')).toBe('csharp')
+    expect(languageKeyForExt('kt')).toBe('kotlin')
+    expect(languageKeyForExt('swift')).toBe('swift')
+    expect(languageKeyForExt('txt')).toBeNull()
+    expect(languageKeyForExt('log')).toBeNull()
+    expect(languageKeyForExt('')).toBeNull()
+  })
+})
+
+describe('pdf preview kind', () => {
+  it('routes only .pdf to the browser-native preview', () => {
+    expect(isPdfExt('.pdf')).toBe(true)
+    expect(isPdfExt('.PDF')).toBe(false)
+    expect(isPdfExt('.docx')).toBe(false)
+    expect(isPdfExt('')).toBe(false)
+  })
+})
+
+describe('image preview kind', () => {
+  it('routes supported image extensions before binary probing', () => {
+    expect(isImageExt('.png')).toBe(true)
+    expect(isImageExt('.jpg')).toBe(true)
+    expect(isImageExt('.svg')).toBe(true)
+    expect(isImageExt('.avif')).toBe(true)
+    expect(isImageExt('.pdf')).toBe(false)
+    expect(isImageExt('')).toBe(false)
+  })
+})