I wish test running was modular/cacheable

[matanlurey]

For example, I have a PR where I removed some unused code in _test.dart files (8 to be precise), but the test runner will execute all of the tests again (locally, and on travis). I wish there was a way we could store the test graph and avoid re-running tests that couldn't have changed.

(I realize this is hard, related to #967, but even worse - we'd have to for example include the chrome binary as an external dependency and track if it changes)

[jakemac53]

There is also another issue of people depending on external things we can't track in their tests. The simple example is a goldens test.

[matanlurey]

I realize we become Bazel at some point, but I guess we could have input globs?

[jakemac53]

I think if we could just override what dart:io does that would be ideal, I know there was some talk of that but I don't know if it actually became a thing or not.

That would still require more tight integration with package:test as well though.