How to solve 'could not find package integration_test in the Flutter SDK' error

It is likely due to your network problem. Because the output says (server unavailable).

Ways to debug this:

  1. Try curl to see whether your command line can connect to network.
  2. Also try, for example, curl (or, try to curl the actual url your pub get is trying to access.

This may due to, for example, your network is broken. Or because you have a broken VPN, broken proxy, etc.

For me had to comment out sdk part like so:

   # sdk: flutter

I had the same error after changing my channel from master to stable. I was able to fix it by removing (or commenting out) the following library from pubspec.yaml

#  integration_test:
#    sdk: flutter

I experienced this when I was trying to setup a flutter web project without enabling flutter web on my PC. I enabled flutter for web and everything was okay.