运行测试时总是出现这个错误

[master-lzh]

../../AppData/Local/Pub/Cache/hosted/pub.dartlang.org/fl_chart-0.8.7/lib/src/extensions/canvas_extension.dart:6:1: Error: This requires the 'extension-methods' language feature to be enabled.
Try updating your pubspec.yaml to set the minimum SDK constraint to 2.6 or higher, and running 'pub get'.

我pubspec.yaml里面已经把环境改成了：

environment:
  sdk: ">=2.7.0 <3.0.0"

但是还是出现这种错误，请问有什么解决方案吗