Migrate to Dart 3 (#210) Fix https://github.com/google/file.dart/issues/209 I also made sure `dart analyzer` result is perfect. `abstract class` => `mixin`. They can't be `mixin class` because then they need to expose/re-implement dozens of methods. 
A monorepo for the package:file and package:file_testing packages.
| Package | Description | Published Version |
|---|---|---|
| file | A pluggable, mockable file system abstraction for Dart. |  |
| file_testing | Testing utilities for package:file. |  |
