報錯資訊：

Because every version of flutter_test from sdk depends on collection 1.14.11 and flutter_app depends on collection 1.14.6, flutter_test from sdk is forbidden.
So, because flutter_app depends on flutter_test any from sdk, version solving failed.

collection 版本不一致，修改依賴：
在pubspec.lock(pub檔案)下找到collection

 collection:
      dependency: transitive
      description:
        name: collection
        url: "https://pub.dartlang.org"
      source: hosted
      version: "1.14.11"

在.yaml檔案裡，dependencies下，與上面保持一致

collection: ^1.14.11

Packages get 如果報：

Expected a key while parsing a block mapping.
   collection:
   ^
 

可不用管，直接run就好。
如果報SDK版本衝突，把對應的依賴，按照上面的collection的操作依賴，版本升級就好，如果不知道最新版本是多少，安利一波：flutter各種依賴