fix(browser): fix upload File instance (#9294)

Author: hi-ogawa

packages/browser/src/client/tester/locators/index.ts

@@ -117,7 +117,8 @@ export abstract class Locator {
       return {
         name: file.name,
         mimeType: file.type,
-        base64: bas64String,
+        // strip prefix `data:[<media-type>][;base64],`
+        base64: bas64String.slice(bas64String.indexOf(',') + 1),
       }
     })
     return this.triggerCommand<void>('__vitest_upload', this.selector, await Promise.all(filesPromise), options)

test/browser/test/userEvent.test.ts

@@ -895,6 +895,7 @@ describe('uploading files', async () => {
     const uploadedFile = input.files[0]
     expect(uploadedFile.name).toBe('hello.png')
     expect(uploadedFile.type).toBe('image/png')
+    expect(await uploadedFile.text()).toBe('hello')
   })
 
   test.skipIf(server.provider === 'webdriverio')('can upload several instances of File', async () => {