[REQ] [Dart] Update testing documentation in petstore client sample
Created by: nickmeinhold
Is your feature request related to a problem? Please describe.
The testing documentation is out of date, eg. suggests using pub serve.
Describe the solution you'd like
The documentation and potentially the testing tools to be updated. I plan to go through the sample when I get some time and try and update.
Describe alternatives you've considered
Maybe review the other test folders in samples/client/petstore/dart2/ at the same time and update together.