Support hybrid (browser + custom Dart server) tests

[kevmoo]

Sometimes you'd like to hit custom server code (written in Dart) from a browser test.

See pkg/http as an example.

[nex3]

The example Kevin is referring to is this one, where the test relies on the old test.dart behavior of automatically starting up an echo server.

[ErikGrimes]

More generally, I'd like support for setup that occurs outside the browser. This way I could spin up a set of Docker containers, a Dart server, or whatever else I need to setup for the browser test.

[kevmoo]

@ErikGrimes oooo – I like that scenario. I hit it often myself.

Keep in mind "custom server code" is anything you can run with dart:io, which includes starting/stopping processes

[zoechi]

I use grinder to run custom servers and https://pub.dartlang.org/packages/bwu_docker to run Docker containers before running pub run test

[ErikGrimes]

@kevmoo Ahh, for some reason my brain translated custom server code to Dart only scripts! Are you open to PR's for this? A relatively straightforward approach would be to mimic the Process api.

[nex3]

I don't think we're going to be able to design a satisfactory API here without some sort of plugin infrastructure being exposed. I want to sit on it for now.

[nex3]

Closing this as a duplicate of #109.