error: Target of URI doesn't exist: 'package:test/test.dart'
If you've upgraded to a recent master, you'll find that flutter_test has removed its dependency on package:test. The package hasn't been removed or renamed, but you will need to specifically add it to you dev_dependencies in your pubspec now:
dev_dependencies: test: ^1.5.1The test_api package is just used to unify the versioning and reduce the depencies of flutter_test. It didn't replace package:test. There are also no breaking changes in any of these newer test versions.
The problem for me targeted URI doesn't exist was due to lib folder inside test package was not available atfile:///E:/APPS/flutter/flutter/.pub-cache/hosted/pub.dartlang.org/dartz-0.9.2/lib/so I downloaded it from GitHub and add it there manually and restarted the IDE. And It worked.